Reverse a string: Difference between revisions
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{{task|String manipulation}}
;Task:
Take a string and reverse it.
;Extra credit:
Preserve Unicode combining characters.
For example, "as⃝df̅" becomes "f̅ds⃝a", not "̅fd⃝sa".
{{Template:Strings}}
<br><br>
=={{header|0815}}==
This program reverses each line of its input.
<syntaxhighlight lang="0815">}:r: Start reader loop.
!~>& Push a character to the "stack".
<:a:=- Stop reading on newline.
^:r:
@> Rotate the newline to the end and enqueue a sentinel 0.
{~ Dequeue and rotate the first character into place.
}:p:
${~ Print the current character until it's 0.
^:p:
#:r: Read again.</syntaxhighlight>
{{out}}
<syntaxhighlight lang="bash">echo -e "foo\nbar" | 0815 rev.0
oof
rab</syntaxhighlight>
=={{header|11l}}==
<syntaxhighlight lang="11l">reversed(string)</syntaxhighlight>
=={{header|360 Assembly}}==
For maximum compatibility, this program uses only the basic instruction set (S/360)
and an ASSIST macro (XPRNT) to keep the code as short as possible.
<syntaxhighlight lang="360asm">* Reverse a string 21/05/2016
REVERSE CSECT
USING REVERSE,R13 base register
B 72(R15) skip savearea
DC 17F'0' savearea
STM R14,R12,12(R13) prolog
ST R13,4(R15) "
ST R15,8(R13) "
LR R13,R15 "
MVC TMP(L'C),C tmp=c
LA R8,C @c[1]
LA R9,TMP+L'C-1 @tmp[n-1]
LA R6,1 i=1
LA R7,L'C n=length(c)
LOOPI CR R6,R7 do i=1 to n
BH ELOOPI leave i
MVC 0(1,R8),0(R9) substr(c,i,1)=substr(tmp,n-i+1,1)
LA R8,1(R8) @c=@c+1
BCTR R9,0 @tmp=@tmp-1
LA R6,1(R6) i=i+1
B LOOPI next i
ELOOPI XPRNT C,L'C print c
L R13,4(0,R13) epilog
LM R14,R12,12(R13) "
XR R15,R15 "
BR R14 exit
C DC CL12'edoC attesoR'
TMP DS CL12
REGEQU
END REVERSE</syntaxhighlight>
{{out}}
<pre>
Rosetta Code
</pre>
This second example uses MVCIN introduced in S/370 architecture.
<syntaxhighlight lang="360asm">* Reverse a string 25/04/2020
REVERSEI CSECT
USING REVERSEI,R13 base register
B 72(R15) skip savearea
DC 17F'0' savearea
STM R14,R12,12(R13) prolog
ST R13,4(R15) "
ST R15,8(R13) "
LR R13,R15 "
MVCIN BB,AA+L'AA-1
XPRNT BB,L'BB print bb
L R13,4(0,R13) epilog
LM R14,R12,12(R13) "
XR R15,R15 "
BR R14 exit
AA DC CL12'edoC attesoR' a
BB DS CL(L'AA) b
REGEQU
END REVERSEI</syntaxhighlight>
{{out}}
<pre>
Rosetta Code
</pre>
=={{header|8080 Assembly}}==
This is a routine that reverses a string with a terminator in place.
Back when the 8080 was commonly used, there wasn't really a set standard about how to store strings.
Zero-terminated strings were already in use by the C language (and therefore, programs written in it).
CP/M, on the other hand, used <code>$</code> as a string terminator. (Later versions would even allow
the programmer to set it himself with a system call!) Therefore, to allow for some flexibility,
this routine also allows you to set it yourself, using the A register.
There were other ways of representing strings, like setting the high bit of the last character to mark
the end (saves a byte per string, but halves the character set size), or prepending the length
(making it unnecessary to scan through the string to find the end, but capping string size at
255 bytes), or even storing tuples of lengths and pointers (easy for a garbage collector to manage).
These are not supported, as they would be completely different routines, though the <code>arrayrev</code>
entry point will reverse a byte array if you already have its start and end.
Unicode is not supported either. While it wouldn't be impossible to do, I think writing a full UTF-8
implementation is beyond the scope of the task.
<syntaxhighlight lang="8080asm"> org 100h
jmp test
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reverse a string under HL in place
;; strrev0: reverse a zero-terminated string
;; strrev: reverse a string terminated by the value in A
;; arrayrev: reverse bytes starting at DE and ending at HL
;; Destroys a, b, d, e, h, l registers.
strrev0: xra a ; Zero A
strrev: mov d,h ; Copy string begin to DE
mov e,l
dcx h
strrev_end: inx h ; Find string end in HL
cmp m
jnz strrev_end
dcx h ; Point HL to last character
arrayrev: mov a,h ; If HL<DE, we're done
cmp d
rc
mov a,l
cmp e
rc
ldax d ; Get low character in string
mov b,m ; Get high character in string
mov m,a ; Swap them
mov a,b
stax d
inx d ; Move the low pointer up,
dcx h ; and the high pointer down
jmp arrayrev
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Test code (CP/M): ask the user for a string, and reverse it
prompt: db " :gnirts a retne esaelP$"
bufdef: db 127, 0
buf: ds 128 ; one extra byte that will remain 0
newline: lxi d,newline_str
mvi c,9
jmp 5
newline_str: db 13, 10, "$"
test: ;; Reverse and output the prompt
mvi a,'$' ; CP/M string is $-terminated
lxi h,prompt ; Reverse the string
call strrev
lxi d,prompt ; Output the string
mvi c,9
call 5
;; Get input and reverse it
lxi d,bufdef
mvi c,10
call 5
call newline
lxi h,buf
call strrev0 ; 0-terminated due to buffer definition
;; Output reversed input
lxi h,buf
loop: mov e,m
xra a
ora e
rz ; Stop when done
mvi c,2
push h
call 5
pop h
inx h
jmp loop</syntaxhighlight>
=={{header|8th}}==
In 8th strings are UTF-8 and the language retains characters per-se:
<syntaxhighlight lang="forth">
"abc" s:rev
</syntaxhighlight>
{{out}}
<tt>"cba"</tt>
=={{header|ACL2}}==
<syntaxhighlight lang="lisp">(reverse "hello")</syntaxhighlight>
ACL2 does not support unicode.
=={{header|Action!}}==
<syntaxhighlight lang="action!">PROC Reverse(CHAR ARRAY src,dst)
BYTE i,j
i=1 j=src(0) dst(0)=j
WHILE j>0
DO
dst(j)=src(i)
i==+1 j==-1
OD
RETURN
PROC Test(CHAR ARRAY src)
CHAR ARRAY dst(40)
Reverse(src,dst)
PrintF("'%S' -> '%S'%E",src,dst)
RETURN
PROC Main()
Test("Hello World!")
Test("123456789")
Test("!noitcA iratA")
RETURN</syntaxhighlight>
{{out}}
[https://gitlab.com/amarok8bit/action-rosetta-code/-/raw/master/images/Reverse_a_string.png Screenshot from Atari 8-bit computer]
<pre>
'Hello World!' -> '!dlroW olleH'
'123456789' -> '987654321'
'!noitcA iratA' -> 'Atari Action!'
</pre>
=={{header|ActionScript}}==
<
{
var reversed:String = new String();
Line 16 ⟶ 253:
{
return string.split('').reverse().join('');
}</syntaxhighlight>
=={{header|Ada}}==
<
procedure Reverse_String is
Line 33 ⟶ 269:
begin
Put_Line (Reverse_It (Get_Line));
end Reverse_String;</
=={{header|Agda}}==
Using the Agda standard library, version 1.7 .
<syntaxhighlight lang="agda">
module ReverseString where
open import Data.String using (String ; fromList ; toList)
open import Data.List using (reverse)
reverse-string : String → String
reverse-string s = fromList (reverse (toList s))
</syntaxhighlight>
=={{header|Aime}}==
<syntaxhighlight lang="aime">o_(b_reverse("Hello, World!"), "\n");</syntaxhighlight>
=={{header|ALGOL 68}}==
{{works with|ALGOL 68|Standard - no extensions to language used}}
{{works with|ALGOL 68G|Any - tested with release mk15-0.8b.fc9.i386}}
{{works with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release 1.8.8d.fc9.i386}}
<
FOR i TO UPB s OVER 2 DO
CHAR c = s[i];
Line 52 ⟶ 302:
reverse(text);
print((text, new line))
)</
{{out}}
<pre>
was I tac a ti saW
</pre>
==
<syntaxhighlight lang="amazing hopper">
#include <hopper.h>
main:
s="mañana será otro día"
reverse(s),strtoutf8, println
{0}return
</syntaxhighlight>
{{out}}
<pre>
aíd orto áres anañam
</pre>
=={{header|Apex}}==
<syntaxhighlight lang="java">
String str = 'Hello World!';
str = str.reverse();
system.debug(str);
</syntaxhighlight>
=={{header|APL}}==
<syntaxhighlight lang="apl"> ⌽'asdf'
fdsa</syntaxhighlight>
=={{header|AppleScript}}==
<syntaxhighlight lang="applescript">reverseString("Hello World!")
on
reverse of characters of str as string
end reverseString</syntaxhighlight>
'''NB.''' Since coercing lists to string involves the interpolation of the current value of AppleScript's text item delimiters between the list items, it's considered best practice to set the delimiters ''explicitly'' to their default value of <code>{""}</code> (or just <code>""</code>) before doing an operation like this, in case they've been set to something else elsewhere in the script:
<syntaxhighlight lang="applescript">reverseString("Hello World!")
on reverseString(str)
set astid to AppleScript's text item delimiters
set AppleScript's text item delimiters to ""
set reversedString to reverse of characters of str as text
set AppleScript's text item delimiters to astid
return reversedString
end reverseString</syntaxhighlight>
----
Or, if we want a polymorphic '''reverse()''' for both strings and lists, we can define it either in terms of a generic fold/reduce, or using the built-in method for lists:
<syntaxhighlight lang="applescript">-- Using either a generic foldr(f, a, xs)
-- reverse1 :: [a] -> [a]
on reverse1(xs)
script rev
on |λ|(a, x)
a & x
end |λ|
end script
if class of xs is text then
foldr(rev, {}, xs) as text
else
foldr(rev, {}, xs)
end if
end reverse1
-- or the built-in reverse method for lists
-- reverse2 :: [a] -> [a]
on reverse2(xs)
if class of xs is text then
(reverse of characters of xs) as text
else
reverse of xs
end if
end reverse2
-- TESTING reverse1 and reverse2 with same string and list ---------------------------------------------------------------------------
on run
script test
on |λ|(f)
map(f, ["Hello there !", {1, 2, 3, 4, 5}])
end |λ|
end script
map(test, [reverse1, reverse2])
end run
-- GENERIC FUNCTIONS ---------------------------------------------------------------------------
-- foldr :: (a -> b -> a) -> a -> [b] -> a
on foldr(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with i from lng to 1 by -1
set v to |λ|(v, item i of xs, i, xs)
end repeat
return v
end tell
end foldr
-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs, i, xs)
end repeat
return lst
end tell
end map
-- Lift 2nd class handler function into 1st class script wrapper
-- mReturn :: Handler -> Script
on mReturn(f)
if class of f is script then
f
else
script
property |λ| : f
end script
end if
end mReturn</syntaxhighlight>
{{Out}}
<syntaxhighlight lang="applescript">{{"! ereht olleH", {5, 4, 3, 2, 1}},
{"! ereht olleH", {5, 4, 3, 2, 1}}}</syntaxhighlight>
=={{header|Arturo}}==
<syntaxhighlight lang="rebol">str: "Hello World"
print reverse str</syntaxhighlight>
{{out}}
<pre>dlroW olleH</pre>
=={{header|AutoHotkey}}==
; <nowiki>"Normal" version:</nowiki>
<syntaxhighlight lang="autohotkey">MsgBox % reverse("asdf")
reverse(string)
Line 85 ⟶ 455:
reversed := A_LoopField . reversed
Return reversed
}</
; <nowiki>A ''much'' slower version:</nowiki>
<syntaxhighlight lang="ahk">Reverse(String){ ; credit to Rseding91
If (A_IsUnicode){
SLen := StrLen(String) * 2
VarSetCapacity(RString,SLen)
Loop,Parse,String
NumPut(Asc(A_LoopField),RString,SLen-(A_Index * 2),"UShort")
} Else {
SLen := StrLen(String)
VarSetCapacity(RString,SLen)
Loop,Parse,String
NumPut(Asc(A_LoopField),RString,SLen-A_Index,"UChar")
}
VarSetCapacity(RString,-1)
Return RString
}</syntaxhighlight>
=={{header|AutoIt}}==
<
$mystring="asdf"
$reverse_string = ""
Line 99 ⟶ 489:
Next
MsgBox(0, "Reversed string is:", $reverse_string)</syntaxhighlight>
=={{header|
<syntaxhighlight lang="avail">"asfd" reversed</syntaxhighlight>
=={{header|AWK}}==
<syntaxhighlight lang="awk">function reverse(s)
{
p = ""
Line 113 ⟶ 504:
BEGIN {
print reverse("edoCattesoR")
}</
;Recursive
<syntaxhighlight lang="awk">function reverse(s ,l)
{
l = length(s)
Line 125 ⟶ 515:
BEGIN {
print reverse("edoCattesoR")
}</
;using split, then joining in front:
<syntaxhighlight lang="awk"># Usage: awk -f reverse.awk -v s=Rosetta
function rev(s, i,len,a,r) {
len = split(s, a, "")
#for (i in a) r = a[i] r # may not work - order is not guaranteed !
for (i=1; i<=len; i++) r = a[i] r
return r
}
BEGIN {
if(!s) s = "Hello, world!"
print s, "<-->", rev(s)
}
</syntaxhighlight>
{{out}}
Rosetta <--> attesoR
=={{header|Babel}}==
This example will handle UTF-8 encoded Unicode but doesn't handle combining characters.
<syntaxhighlight lang="babel">strrev: { str2ar ar2ls reverse ls2lf ar2str }</syntaxhighlight>
*str2ar - this operator converts a UTF-8 encoded string to an array of Unicode codepoints
*ar2ls - this operator converts the array to a linked-list
*reverse - this operator reverses a linked-list
*ls2lf - this operator undoes the effect of ar2ls
*ar2str - this operator undoes the effect of str2ar
=={{header|BaCon}}==
<syntaxhighlight lang="freebasic">OPTION UTF8 TRUE
s$ = "asdf"
PRINT REVERSE$(s$)</syntaxhighlight>
Unicode preservation works in BaCon 3.6 and higher.
=={{header|BASIC}}==
==={{header|Applesoft BASIC}}===
<syntaxhighlight lang="applesoftbasic">10 A$ = "THE FIVE BOXING WIZARDS JUMP QUICKLY"
20 GOSUB 100REVERSE
30 PRINT R$
40 END
100 REMREVERSE A$
110 R$ = ""
120 FOR I = 1 TO LEN(A$)
130 R$ = MID$(A$, I, 1) + R$
140 NEXT I
150 RETURN</syntaxhighlight>
==={{header|BASIC256}}===
<syntaxhighlight lang="vb">s = "asdf"
print "'"; s; "' reversed is '"; reverse(s); "'"
end
function reverse(a)
b = ""
for i = 1 to length(a)
b = mid(a, i, 1) + b
next i
return b
end function</syntaxhighlight>
{{out}}
<pre>'asdf' reversed is 'fdsa'</pre>
==={{header|Commodore BASIC}}===
{{works with|Commodore BASIC|3.5,7.0}}
Commodore BASIC 3.5 turned MID$ into an lvalue function, and assigning a string of the same length to MID$ replaces the characters instead of allocating a new string, so the reversal can be done in-place:
<syntaxhighlight lang="basic">
100 INPUT "STRING";S$
110 FOR I=1 TO INT(LEN(S$)/2)
120 : J=LEN(S$)+1-I
130 : T$=MID$(S$,I,1)
140 : MID$(S$,I,1) = MID$(S$,J,1)
150 : MID$(S$,J,1) = T$
160 NEXT I
170 PRINT S$</syntaxhighlight>
{{Out}}
<pre>STRING? THIS IS A TEST
TSET A SI SIHT
READY.</pre>
==={{header|IS-BASIC}}===
<syntaxhighlight lang="is-basic">100 INPUT PROMPT "String: ":TX$
120 LET REV$=""
130 FOR I=LEN(TX$) TO 1 STEP-1
140 LET REV$=REV$&TX$(I)
150 NEXT
160 PRINT REV$</syntaxhighlight>
==={{header|QuickBASIC}}===
{{works with|QBasic|1.1}}
{{works with|QuickBasic|4.5}}
<
b$ = ""
for i = 1 to len(a$)
Line 135 ⟶ 616:
next i
reverse$ = b$
end function</
==={{header|Sinclair ZX81 BASIC}}===
<syntaxhighlight lang="basic">10 INPUT S$
20 LET T$=""
30 FOR I=LEN S$ TO 1 STEP -1
40 LET T$=T$+S$(I)
50 NEXT I
60 PRINT T$</syntaxhighlight>
==={{header|True BASIC}}===
<syntaxhighlight lang="qbasic">FUNCTION reverse$(a$)
LET b$ = ""
FOR i = 1 TO LEN(a$)
LET b$ = (a$)[i:i+1-1] & b$
NEXT i
LET reverse$ = b$
END FUNCTION
LET s$ = "asdf"
PRINT "'"; s$; "' reversed is '"; reverse$(s$); "'"
END</syntaxhighlight>
{{out}}
<pre>'asdf' reversed is 'fdsa'</pre>
==={{header|XBasic}}===
{{works with|Windows XBasic}}
<syntaxhighlight lang="qbasic">PROGRAM "progname"
VERSION "0.0000"
DECLARE FUNCTION Entry ()
DECLARE FUNCTION reverse$ (a$)
FUNCTION Entry ()
s$ = "asdf"
PRINT "'"; s$; "' reversed is '"; reverse$(s$); "'"
END FUNCTION
FUNCTION reverse$ (a$)
b$ = ""
FOR i = 1 TO LEN(a$)
b$ = MID$(a$, i, 1) + b$
NEXT i
RETURN b$
END FUNCTION
END PROGRAM</syntaxhighlight>
{{out}}
<pre>'asdf' reversed is 'fdsa'</pre>
==={{header|Yabasic}}===
<syntaxhighlight lang="vb">s$ = "asdf"
print "'", s$, "' reversed is '", reverse$(s$), "'"
end
sub reverse$(a$)
b$ = ""
for i = 1 to len(a$)
b$ = mid$(a$, i, 1) + b$
next i
return b$
end sub</syntaxhighlight>
{{out}}
<pre>'asdf' reversed is 'fdsa'</pre>
=={{header|Batch File}}==
<
setlocal enabledelayedexpansion
call :reverse %1 res
Line 154 ⟶ 697:
set str=%str:~1%
set %2=%chr%!%2!
goto loop</
=={{header|BBC BASIC}}==
<
END
Line 165 ⟶ 708:
B$ += MID$(A$,C%,1)
NEXT
= B$</
=={{header|Beef}}==
Beef does not have a built-in Reverse method for strings, however one can 'extend' the builtin String class to provide a Reverse function.
<syntaxhighlight lang="csharp">using System;
namespace System
{
extension String
{
public void Reverse()
{
int i = 0;
int j = mLength - 1;
while (i < j)
{
Swap!(Ptr[i++], Ptr[j--]);
}
}
}
}
namespace StringReverse
{
class Program
{
static void Main()
{
String s = scope .("abcdef");
s.Reverse();
Console.WriteLine(s);
}
}
}
</syntaxhighlight>
=={{header|Befunge}}==
Reads a line from stdin and write the reverse to stdout. Can be made to repeat indefinitely by removing the final <tt>@</tt> command.
<syntaxhighlight lang="befunge">55+~>:48>*#8\#4`#:!#<#~_$>:#,_@</syntaxhighlight>
=={{header|Binary Lambda Calculus}}==
This 9 byte program, featured on https://www.ioccc.org/2012/tromp/hint.html, reverses its input in byte-oriented BLC:
<pre>16 46 80 17 3e f0 b7 b0 40</pre>
=={{header|BQN}}==
BQN has a reverse builtin, given as <code>⌽</code>.
<syntaxhighlight lang="bqn"> ⌽"racecar"
"racecar"</syntaxhighlight>
=={{header|Bracmat}}==
<syntaxhighlight lang="bracmat"> ( reverse
= L x
. :?L
& @( !arg
: ?
( %?x
& utf$!x
& !x !L:?L
& ~`
)
?
)
| str$!L
)
& out$reverse$Ελληνικά</syntaxhighlight>
{{out}}
<pre>άκινηλλΕ</pre>
=={{header|Brainf***}}==
<syntaxhighlight lang="bf">[-]>,[>,]<[.<]</syntaxhighlight>
Another solution:
<syntaxhighlight lang="bf">,----- ----- [+++++ +++++ > , ----- -----] If a newline is hit counter will be zero and input loop ends
<[.<] run all chars backwards and print them
just because it looks good we print CRLF
+++++ +++++ +++ . --- .</
=={{header|Brat}}==
<
=={{header|Burlesque}}==
<syntaxhighlight lang="burlesque">
"Hello, world!"<-
</syntaxhighlight>
=={{header|C}}==
<
#include <stdlib.h>
#include <locale.h>
#include <wchar.h>
const char *sa = "abcdef";
const char *su = "as⃝df̅"; /* Should be in your native locale encoding. Mine is UTF-8 */
int is_comb(wchar_t c)
Line 219 ⟶ 816:
}
wchar_t* mb_to_wchar(const char *s)
{
wchar_t *u;
Line 230 ⟶ 827:
}
wchar_t* ws_reverse(const wchar_t* u)
{
size_t len, i, j;
Line 247 ⟶ 844:
}
char *mb_reverse(const char *in)
{
size_t len;
Line 268 ⟶ 865:
printf("%s => %s\n", su, mb_reverse(su));
return 0;
}</syntaxhighlight>
{{out}}
<pre>abcdef => fedcba
as⃝df̅ => f̅ds⃝a</pre>
<syntaxhighlight lang="c">#include <glib.h>
gchar *srev (const gchar *s) {
if (g_utf8_validate(s,-1,NULL)) {
return g_utf8_strreverse (s,-1);
} }
// main
int main (void) {
const gchar *t="asdf";
const gchar *u="as⃝df̅";
printf ("%s\n",srev(t));
printf ("%s\n",srev(u));
return 0;
}</syntaxhighlight>
=={{header|C sharp}}==
C# does not have a built-in Reverse method for strings, and cannot reverse them in place because they are immutable. One way to implement this is to convert the string to an array of characters, reverse that, and return a new string from the reversed array:
<syntaxhighlight lang="csharp">static string ReverseString(string input)
{
char[] inputChars = input.ToCharArray();
Array.Reverse(inputChars);
return new string(inputChars);
}</syntaxhighlight>
As of .Net 3.5 the LINQ-to-objects allows the Reverse() extension method to be called on a string, since String implements the IEnumerable<char> interface. Because of this, the return type of Reverse is IEnumerable<char>. Fortunately, LINQ also provides the ToArray extension method, which can be used in conjunction with the constructor of string that accepts a char array:
<syntaxhighlight lang="csharp">using System.Linq;
// ...
return new string(input.Reverse().ToArray());
// ...</syntaxhighlight>
'''Version supporting combining characters:'''
System.Globalization.StringInfo provides a means of separating a string into individual graphemes.
<syntaxhighlight lang="csharp">public string ReverseElements(string s)
{
// In .NET, a text element is series of code units that is displayed as one character, and so reversing the text
// elements of the string correctly handles combining character sequences and surrogate pairs.
var elements = System.Globalization.StringInfo.GetTextElementEnumerator(s);
return string.Concat(AsEnumerable(elements).OfType<string>().Reverse());
}
// Wraps an IEnumerator, allowing it to be used as an IEnumerable.
public IEnumerable AsEnumerable(IEnumerator enumerator)
{
while (enumerator.MoveNext())
yield return enumerator.Current;
}</syntaxhighlight>
=={{header|C++}}==
<syntaxhighlight lang="cpp">#include <string>
#include <iostream>
#include <algorithm>
int main() {
std::string s;
std::getline(std::cin, s);
std::reverse(s.begin(), s.end()); // modifies s
std::cout << s <<
}</syntaxhighlight>
=={{header|
<pre>USER>Write $Reverse("Hello, World")
dlroW ,olleH</pre>
=={{header|Ceylon}}==
<syntaxhighlight lang="ceylon">
shared void run() {
while(true) {
process.write("> ");
String? text = process.readLine();
if (is String text) {
print(text.reversed);
}
else {
break;
}
}
}
</syntaxhighlight>
=={{header|Clipper}}==
Works with versions since 5, because ''LOCAL'' variables and the ''+='' operator was not implemented before.
<syntaxhighlight lang="clipper">FUNCTION Reverse(sIn)
LOCAL sOut := "", i
FOR i := Len(sIn) TO 1 STEP -1
sOut += Substr(sIn, i, 1)
NEXT
RETURN sOut</syntaxhighlight>
=={{header|Clojure}}==
=== A Simple implementation with the magic of "conj" function ===
<syntaxhighlight lang="lisp">
(defn reverse-string [s]
"Returns a string with all characters in reverse"
(apply str (reduce conj '() s)))
</syntaxhighlight>
=== Other alternatives (resorting to the "reverse" function in the standard library)===
For normal strings, the reverse function can be used to do the bulk of the work. However, it returns a character sequence, which has to be converted back to a string.
a) <syntaxhighlight lang="lisp">(defn str-reverse [s] (apply str (reverse s)))</syntaxhighlight>
b) <syntaxhighlight lang="lisp">(apply str (interpose " " (reverse (.split "the quick brown fox" " "))))</syntaxhighlight>
=== Supporting combining characters ===
Handling combining characters present a trickier task. We need to protect the relative ordering of the combining character and the character to its left. Thus, before reversing, the characters need to be grouped.
<syntaxhighlight lang="lisp">(defn combining? [c]
(let [type (Character/getType c)]
;; currently hardcoded to the types taken from the sample string
Line 334 ⟶ 1,003:
"Unicode-safe string reverse"
[s]
(apply str (apply concat (reverse (group s)))))</
{{out}}
<pre>
user=> s
Line 346 ⟶ 1,014:
user=>
</pre>
=={{header|CLU}}==
<syntaxhighlight lang="clu">reverse = proc (s: string) returns (string)
rslt: array[char] := array[char]$predict(1,string$size(s))
for c: char in string$chars(s) do
array[char]$addl(rslt,c)
end
return(string$ac2s(rslt))
end reverse
start_up = proc ()
po: stream := stream$primary_output()
stream$putl(po, reverse("!dlrow ,olleH"))
end start_up</syntaxhighlight>
{{out}}
<pre>Hello, world!</pre>
=={{header|COBOL}}==
<syntaxhighlight lang="cobol">FUNCTION REVERSE('QWERTY')</syntaxhighlight>
=={{header|CoffeeScript}}==
<syntaxhighlight lang="javascript">"qwerty".split("").reverse().join ""</syntaxhighlight>
=={{header|ColdFusion}}==
You can reverse anything that can be written to the document in hashmarks (i.e. strings, numbers, now( ), etc.).
<
<cfset myString = reverse( myString ) /></
=={{header|Common Lisp}}==
<syntaxhighlight lang
=={{header|Component Pascal}}==
BlackBox Component Builder
<syntaxhighlight lang="oberon2">
MODULE BbtReverseString;
IMPORT StdLog;
PROCEDURE ReverseStr(str: ARRAY OF CHAR): POINTER TO ARRAY OF CHAR;
VAR
top,middle,i: INTEGER;
c: CHAR;
rStr: POINTER TO ARRAY OF CHAR;
BEGIN
NEW(rStr,LEN(str$) + 1);
top := LEN(str$) - 1; middle := (top - 1) DIV 2;
FOR i := 0 TO middle DO
rStr[i] := str[top - i];
rStr[top - i] := str[i];
END;
IF ODD(LEN(str$)) THEN rStr[middle + 1] := str[middle + 1] END;
RETURN rStr;
END ReverseStr;
PROCEDURE Do*;
VAR
x: CHAR;
BEGIN
StdLog.String("'asdf' reversed:> ");StdLog.String(ReverseStr("asdf"));StdLog.Ln
END Do;
END BbtReverseString.
</syntaxhighlight>
Execute: ^Q BbtReverseString.Do<br/>
{{Out}}
<pre>
'asdf' reversed:> fdsa
</pre>
=={{header|Cowgol}}==
<syntaxhighlight lang="cowgol">include "cowgol.coh";
include "strings.coh";
# Reverse a string in place
sub StrRev(s: [uint8]): (r: [uint8]) is
r := s;
var e := s;
while [e] != 0 loop
e := @next e;
end loop;
e := @prev e;
while e > s loop
var c := [s];
[s] := [e];
[e] := c;
s := @next s;
e := @prev e;
end loop;
end sub;
# Test
var buf: uint8[32];
var str: [uint8] := "\nesreveR";
CopyString(str, &buf[0]);
print(StrRev(&buf[0]));</syntaxhighlight>
{{out}}
<pre>Reverse</pre>
=={{header|Crystal}}==
<syntaxhighlight lang="ruby"># version 0.21.1
strings = ["asdf", "as⃝df̅"]
strings.each do |s|
puts "#{s} -> #{s.reverse}"
end</syntaxhighlight>
{{out}}
<pre>
asdf -> fdsa
as⃝df̅ -> f̅ds⃝a
</pre>
=={{header|D}}==
<syntaxhighlight lang="d">void main() {
import std.range, std.conv;
string s1 = "hello"; // UTF-8
assert(s1.retro.text == "olleh");
wstring s2 = "hello"w; // UTF-16
assert(s2.retro.wtext == "olleh"w);
dstring s3 = "hello"d; // UTF-32
assert(s3.retro.dtext == "olleh"d);
// without using std.range:
dstring s4 = "hello"d;
assert(s4.dup.reverse == "olleh"d); // simple but inefficient (copies first, then reverses)
}</syntaxhighlight>
=={{header|Dart}}==
Since Dart strings are sequences of [http://en.wikipedia.org/wiki/UTF-16 UTF-16] code units, it would not be sufficient to simply reverse the characters in strings, as this would not work with UTF-16 [http://en.wikipedia.org/wiki/UTF-16#Code_points_U.2B10000_to_U.2B10FFFF surrogate pairs] (pairs of UTF-16 code units that represent single characters [http://en.wikipedia.org/wiki/Plane_(Unicode)#Supplementary_Multilingual_Plane outside the Unicode BMP]). However, Dart provides a method to convert strings to sequences of unicode code points (called "runes" in Dart), and these sequences can easily be reversed and used to create new strings, so a string reversal function can be written with a single line of Dart code:
<syntaxhighlight lang="dart">String reverse(String s) => new String.fromCharCodes(s.runes.toList().reversed);</syntaxhighlight>
A more complete example with unit tests would look like this:
<syntaxhighlight lang="dart">import 'package:unittest/unittest.dart';
String reverse(String s) => new String.fromCharCodes(s.runes.toList().reversed);
main() {
group("Reverse a string -", () {
test("Strings with ASCII characters are reversed correctly.", () {
expect(reverse("hello, world"), equals("dlrow ,olleh"));
});
test("Strings with non-ASCII BMP characters are reversed correctly.", () {
expect(reverse("\u4F60\u4EEC\u597D"), equals("\u597D\u4EEC\u4F60"));
});
test("Strings with non-BMP characters are reversed correctly.", () {
expect(reverse("hello, \u{1F310}"), equals("\u{1F310} ,olleh"));
});
});
}</syntaxhighlight>
=={{header|DBL}}==
<syntaxhighlight lang="dbl">K=
STR_OUT=
FOR J=%TRIM(STR_IN) STEP -1 UNTIL 1
DO BEGIN
INCR K
STR_OUT(K:1)=STR_IN(J:1)
END
</syntaxhighlight>
=={{header|Dc}}==
Reversing "Hello world!" which is "22405534230753963835153736737" in Dc's numerical string representaion.<br>
Due to using "~" this example needs GNU Dc or OpenBSD Dc.
<syntaxhighlight lang="dc">22405534230753963835153736737 [ 256 ~ d SS 0<F LS SR 1+ ] d sF x 1 - [ 1 - d 0<F 256 * LR + ] d sF x P</syntaxhighlight>
<pre>
!dlrow olleH
</pre>
=={{header|Delphi}}==
<syntaxhighlight lang="delphi">function ReverseString(const InString: string): string;
var
i: integer;
Line 376 ⟶ 1,196:
for i := Length(InString) downto 1 do
Result := Result + InString[i];
end;</syntaxhighlight>
You could also use this RTL function Introduced in Delphi 6:
<syntaxhighlight lang="delphi">StrUtils.ReverseString</syntaxhighlight>
Another alternative.
<syntaxhighlight lang="delphi">
function Reverse(const s: string): string;
var
i, aLength, ahalfLength: Integer;
c: Char;
begin
Result := s;
aLength := Length(s);
ahalfLength := aLength div 2;
if aLength > 1 then
for i := 1 to ahalfLength do
begin
c := result[i];
result[i] := result[aLength - i + 1];
result[aLength - i + 1] := c;
end;
end;</syntaxhighlight>
All versions has the same perfomance, then StrUtils is recomended.
=={{header|Draco}}==
<syntaxhighlight lang="draco">/* Reverse string in place */
proc nonrec reverse(*char s) void:
*char e;
char t;
e := s;
while e* /= '\e' do
e := e + 1
od;
while
e := e - 1;
s < e
do
t := e*;
e* := s*;
s* := t;
s := s + 1
od
corp
proc nonrec main() void:
*char testString = "!dlrow ,olleH";
reverse(testString);
writeln(testString)
corp</syntaxhighlight>
{{out}}
<pre>Hello, world!</pre>
=={{header|
<syntaxhighlight lang="dt">"asdf" rev</syntaxhighlight>
=={{header|DWScript}}==
See [[Reverse a string#Delphi|Delphi]].
=={{header|
<syntaxhighlight lang="dyalect">let str = "asdf"
func String.Reverse() {
var cs = []
let len = this.Length()
for n in 1..len {
cs.Add(this[len - n])
}
String(values: cs)
}
str.Reverse()</syntaxhighlight>
=={{header|Déjà Vu}}==
<syntaxhighlight lang="dejavu">!print concat chars "Hello"</syntaxhighlight>
{{out}}
<pre>olleH</pre>
=={{header|EasyLang}}==
<syntaxhighlight lang="easylang">
func$ reverse s$ .
a$[] = strchars s$
for i = 1 to len a$[] div 2
swap a$[i] a$[len a$[] - i + 1]
.
return strjoin a$[]
.
print reverse "hello"
</syntaxhighlight>
=={{header|E}}==
[[Category:E examples needing attention]] <!-- Replacing accum, grapheme clusters -->
<syntaxhighlight lang="e">pragma.enable("accumulator")
def reverse(string) {
return accum "" for i in (0..!(string.size())).descending() { _ + string[i] }
}</
=={{header|
<syntaxhighlight lang="lisp">
(define (string-reverse string)
(list->string (reverse (string->list string))))
(string-reverse "ghij")
→ jihg
(string-reverse "un roc lamina l animal cornu")
→ unroc lamina l animal cor nu
</syntaxhighlight>
=={{header|EGL}}==
<syntaxhighlight lang="egl">function reverse( str string ) returns( string )
result string;
for ( i int from StrLib.characterLen( str ) to 1 decrement by 1 )
result ::= str[i:i];
end
return( result );
end</syntaxhighlight>
=={{header|Eiffel}}==
<syntaxhighlight lang="eiffel">class
APPLICATION
create
Line 424 ⟶ 1,329:
my_string: STRING
-- Used for reversal
end</
{{out}}
<pre>
!dlroW olleH
</pre>
=={{header|
<syntaxhighlight lang="ela">reverse_string str = rev len str
where len = length str
rev 0 str = ""
rev n str = toString (str : nn) +> rev nn str
where nn = n - 1
reverse_string "Hello"</syntaxhighlight>
{{out}}<pre>"olleH"</pre>
Another approach is to covert a string to a list, reverse a list and then convert it back to a string:
<syntaxhighlight lang="ela">open string
fromList <| reverse <| toList "Hello" ::: String</syntaxhighlight>
=={{header|Elena}}==
ELENA 4.x:
<syntaxhighlight lang="elena">import system'routines;
import extensions;
import extensions'text;
extension extension
{
reversedLiteral()
= self.toArray().sequenceReverse().summarize(new StringWriter());
}
public program()
{
console.printLine("Hello World".reversedLiteral())
}</syntaxhighlight>
{{out}}
<pre>
dlroW olleH
</pre>
=={{header|Elixir}}==
Elixir handles Unicode graphemes correctly by default.
<syntaxhighlight lang="elixir">
IO.puts (String.reverse "asdf")
IO.puts (String.reverse "as⃝df̅")
</syntaxhighlight>
{{Out}}
<pre>
fdsa
f̅ds⃝a
</pre>
=={{header|Elm}}==
<syntaxhighlight lang="elm">module Main exposing (main)
import Html exposing (Html, text, div, p)
import Html.Attributes exposing (style)
change myText =
text ("reverse " ++ myText
++ " = " ++ String.reverse myText)
main =
div [style "margin" "5%", style "font-size" "1.5em"]
[change "as⃝da"
, p [] [change "a⃝su-as⃝u"]
, p [] [change "Hello!"]
]
</syntaxhighlight>
Link to live demo: https://ellie-app.com/qdg6RP3DGCBa1
{{out}}
<pre>
reverse as⃝da = ad⃝sa
reverse a⃝su-as⃝u = u⃝sa-us⃝a
reverse Hello! = !olleH
</pre>
=={{header|Emacs Lisp}}==
<syntaxhighlight lang="lisp">(reverse "Hello World")</syntaxhighlight>
{{out}}
<pre>
"dlroW olleH"
</pre>
=={{header|Erlang}}==
<syntaxhighlight lang="erlang">1> lists:reverse("reverse!").
"!esrever"</syntaxhighlight>
Erlang also supports binary strings, which uses its binary format. There is no standard function to reverse a binary sequence, but the following one does the job well enough. It works by changing the endianness (from little to big or the opposite) of the whole sequence, effectively reversing the string.
<
Size = size(Bin)*8,
<<T:Size/integer-little>> = Bin,
<<T:Size/integer-big>>.</
{{out}}
<pre>
1> test:reverse(<<"hello">>).
<<"olleh">>
</pre>
=={{header|ERRE}}==
<syntaxhighlight lang="erre">
PROGRAM REVERSE_STRING
PROCEDURE REVERSE(A$->R$)
LOCAL I%
R$=""
FOR I=1 TO LEN(A$) DO
R$=MID$(A$,I,1)+R$
END FOR
END PROCEDURE
BEGIN
A$="THE FIVE BOXING WIZARDS JUMP QUICKLY"
REVERSE(A$->R$)
PRINT(R$)
END PROGRAM
</syntaxhighlight>
=={{header|Euler Math Toolbox}}==
<syntaxhighlight lang="euler math toolbox">
>function strrev (s) := chartostr(fliplr(strtochar(s)))
>strrev("This is a test!")
!tset a si sihT
</syntaxhighlight>
=={{header|Euphoria}}==
<syntaxhighlight lang="euphoria">
include std/sequence.e
printf(1, "%s\n", {reverse("abcdef") })
</syntaxhighlight>
=={{header|Explore}}==
The [[Scratch]] [[Reverse a string#Scratch|solution]], which requires making variables named "i" and "inv" first, works, unmodified:<br>https://i.ibb.co/3c9k641/Reverse-a-string-in-Explore-using-the-Scratch-solution.png
This example uses a special block located in the Strings category:<br>https://i.ibb.co/4pM9G8b/Reverse-a-string-in-Explore-using-a-special-block.png
=={{header|Ezhil}}==
<syntaxhighlight lang="ezhil">
## இந்த நிரல் தரப்படும் சரம் ஒன்றைத் தலைகீழாகத் திருப்பி அச்சிடும்
## உதாரணமாக "abc" என்ற சரம் தரப்பட்டால் அதனைத் திருப்பி "cba" என அச்சிடும்
## "எழில்" மொழியின்மூலம் இரண்டு வகைகளில் இதனைச் செய்யலாம். இரண்டு உதாரணங்களும் இங்கே தரப்பட்டுள்ளன
நிரல்பாகம் திருப்புக (சரம்1)
## முதல் வகை
சரம்2 = ""
@( சரம்1 இல் இ) ஒவ்வொன்றாக
சரம்2 = இ + சரம்2
முடி
பின்கொடு சரம்2
முடி
நிரல்பாகம் மீண்டும்திருப்புக (சரம்1)
## இரண்டாம் வகை
சரநீளம் = len(சரம்1)
சரம்2 = ""
@(எண் = 0, எண் < சரநீளம், எண் = எண் + 1) ஆக
சரம்2 = எடு(சரம்1, எண்) + சரம்2
முடி
பின்கொடு சரம்2
முடி
அ = உள்ளீடு("ஓர் எழுத்துச் சரத்தைத் தாருங்கள் ")
பதிப்பி "நீங்கள் தந்த எழுத்துச் சரம்" அ
பதிப்பி "அதனை முதல் வகையில் திருப்பியுள்ளோம்: " திருப்புக(அ)
பதிப்பி "வேறொரு வகையில் திருப்பியுள்ளோம்: " மீண்டும்திருப்புக(அ)
</syntaxhighlight>
=={{header|F_Sharp|F#}}==
===The function===
<syntaxhighlight lang="fsharp">
// Reverse a string. Nigel Galloway: August 14th., 2019
let strRev α=let N=System.Globalization.StringInfo.GetTextElementEnumerator(α)
List.unfold(fun n->if n then Some(N.GetTextElement(),N.MoveNext()) else None)(N.MoveNext())|>List.rev|>String.concat ""
</syntaxhighlight>
===The Task===
I was a little concerned when entering this task because in the edit window the overline appears above the d, but when previewed it is correctly above the f, using Firefox anyway. Using XTERM the output is correct with the s inside a circle but appears as sO in Firefox.
<syntaxhighlight lang="fsharp">
printfn "%s" (strRev "as⃝df̅")
printfn "%s" (strRev "Nigel")
</syntaxhighlight>
{{out}}
<pre>
f̅ds⃝a
legiN
</pre>
=={{header|Factor}}==
A string is a sequence and there is a default reverse implementation for those.
<
<code>string-reverse</code> preserves graphemes:
<
=={{header|FALSE}}==
This solution does not take into account combination characters:
<syntaxhighlight lang="false">1_
[^$1_=~][]#%
[$1_=~][,]#</syntaxhighlight>
This solution does take into account combination characters (except for half-marks):
<syntaxhighlight lang="false">1_
[^$1_=~][
$$767>\879\>&
1ø$7615>\7620\>&|
1ø$8399>\8428\>&|
[\]?
]#%
[$1_=~][,]#</syntaxhighlight>
=={{header|Fancy}}==
<
=={{header|FBSL}}==
A slow way
<syntaxhighlight lang="qbasic">Function StrRev1(ByVal $p1)
dim $b = ""
REPEAT len(p1)
b = b & RIGHT(p1,1)
p1 = LEFT(p1,LEN(p1)-1)
END REPEAT
return b
End Function
</syntaxhighlight>
A much faster (twice at least) way
<syntaxhighlight lang="qbasic">Function StrRev2(ByVal $p1)
dim $b = "", %i
for i = len(p1) DOWNTO 1
b = b & MID(p1,i,1)
next
return b
End Function</syntaxhighlight>
An even faster way using PEEK, POKE, double-calls and quantity-in-hand
<syntaxhighlight lang="qbasic">Function StrRev3( $s )
FOR DIM x = 1 TO LEN(s) \ 2
PEEK(@s + LEN - x, $1)
POKE(@s + LEN - x, s{x})(@s + x - 1, PEEK)
NEXT
RETURN s
end function
</syntaxhighlight>
An even faster way using the DynC (Dynamic C) mode
<syntaxhighlight lang="c">DynC StringRev($theString) As String
void rev(char *str)
{
int len = strlen(str);
char *HEAD = str;
char *TAIL = str + len - 1;
char temp;
int i;
for ( i = 0; i <= len / 2; i++, HEAD++, TAIL--) {
temp = *HEAD;
*HEAD = *TAIL;
*TAIL = temp;
}
}
char *main(char* theString)
{
rev(theString);
return theString;
}
End DynC</syntaxhighlight>
Using DynASM, the Dynamic Assembler mode.
<syntaxhighlight lang="asm">DYNASM RevStr(BYVAL s AS STRING) AS STRING
// get length of string
// divide by two
// setup pointers to head and tail
// iterate from 1 to (length \ 2)
// swap head with tail
// increment head pointer
// decrement tail pointer
ENTER 0, 0 // = PUSH EBP: MOV EBP, ESP
PUSH EBX // by Windows convention EBX, EDI, ESI must be saved before modification
MOV EAX, s // get string pointer
MOV ECX, EAX // duplicate it
.WHILE BYTE PTR [ECX] <> 0
INC ECX // propagate to tail
.WEND
MOV EDX, ECX // duplicate tail pointer
DEC EDX // set it to last byte before trailing zero
SUB ECX, EAX // get length in ECX in 1 CPU cycle
SHR ECX, 1 // get length \ 2 in 1 CPU cycle; that's the beauty of power-of-two division
.WHILE ECX > 0
MOV BL, [EDX] // no need to XOR; just overwrite BL and BH contents
MOV BH, [EAX] // DynAsm deduces data size from destination register sizes
MOV [EDX], BH // ditto, source register sizes
MOV [EAX], BL
INC EAX // propagate pointers
DEC EDX
DEC ECX // decrement counter
.WEND
// point to start of string again
MOV EAX, s // MOV = 1 CPU cycle, PUSH + POP = 2 CPU cycles
POP EBX // by Windows convention ESI, EDI, EBX must be restored if modified
LEAVE // = POP EBP
RET
END DYNASM
</syntaxhighlight>
=={{header|Fe}}==
In this language, strings are very limited and are not designed to store large text data, so there are no built-in operations to work with strings. But with the C API you can make functions that convert a string to a list and vice versa.
<syntaxhighlight lang="c">
#define MAXSTRINGLEN ( 1024 )
/* chop string to list of single character strings */
static fe_Object* chop(fe_Context *ctx, fe_Object *args) {
char buf[MAXSTRINGLEN];
int len = fe_tostring(ctx, fe_nextarg(ctx, &args), buf, sizeof(buf));
int gc = fe_savegc(ctx);
args = fe_bool(ctx, 0);
while (len > 0) {
buf[len--] = '\0';
args = fe_cons(ctx, fe_string(ctx, buf + len), args);
fe_restoregc(ctx, gc);
fe_pushgc(ctx, args);
}
return args;
}
/* pack list of strings to single string */
static fe_Object* pack(fe_Context *ctx, fe_Object *args) {
char buf[MAXSTRINGLEN], *ptr = buf;
for (args = fe_nextarg(ctx, &args); !fe_isnil(ctx, args);) {
ptr += fe_tostring(ctx, fe_nextarg(ctx, &args), ptr, buf + sizeof(buf) - ptr);
}
return fe_string(ctx, buf);
}
</syntaxhighlight>
So, we can manipulate strings like lists:
<syntaxhighlight lang="clojure">
; reverse list
(= reverse (fn (lst)
(let res nil)
(while lst
(= res (cons (car lst) res))
(= lst (cdr lst)))
res))
; chop string to list, reverse list and pack it back to string
(print (pack (reverse (chop "Hello world!"))))
</syntaxhighlight>
Output:
<syntaxhighlight lang="clojure">
!dlrow olleH
</syntaxhighlight>
=={{header|Fennel}}==
Uses the same methods (and suffers from the same limitations) as [[#Lua|the Lua example]].
<syntaxhighlight lang="fennel">
(let [example :asdf]
(string.reverse example) ; fdsa
(example:reverse) ; fdsa
nil)
</syntaxhighlight>
=={{header|Forth}}==
=== Method 1 ===
<syntaxhighlight lang="forth">: exchange ( a1 a2 -- )
2dup c@ swap c@ rot c! swap c! ;
: reverse ( c-addr u -- )
Line 474 ⟶ 1,737:
repeat 2drop ;
s" testing" 2dup reverse type \ gnitset</
=== Method 2 Using the stack ===
<syntaxhighlight lang="forth">\ reverse a string using the data stack for temporary storage
: mystring ( -- caddr len) S" ABCDEFGHIJKLMNOPQRSTUVWXYZ987654321" ;
: pushstr ( caddr len -- c..c[n]) bounds do I c@ loop ;
: popstr ( c.. c[n] caddr len -- ) bounds do I c! loop ;
: reverse ( caddr len -- ) 2dup 2>r pushstr 2r> popstr ;</syntaxhighlight>
Forth Console Output
<pre>
mystring type ABCDEFGHIJKLMNOPQRSTUVWXYZ987654321 ok
mystring 2dup reverse type 123456789ZYXWVUTSRQPONMLKJIHGFEDCBA ok
</pre>
=== Using the Forth-2012 Xchars wordset to handle multi-byte characters ===
Characters accessed with C@ C! are usually bytes and can therefore only represent characters in 8-bit encodings (e.g., Latin-1). Forth-2012 added the Xchars wordset for dealing with multi-byte encodings such as UTF-8; actually these words are not needed much, because the magic of UTF-8 means that most byte-oriented code works as intended, but the present task is one of the few examples where that is not good enough.
The xchars wordset offers several ways to skin this cat; this is just one way to do it, not necessarily the best one. Because the xchars wordset currently does not support recognizing combining characters, this code does not get extra credit.
<syntaxhighlight lang="forth">: xreverse {: c-addr u -- c-addr2 u :}
u allocate throw u + c-addr swap over u + >r begin ( from to r:end)
over r@ u< while
over r@ over - x-size dup >r - 2dup r@ cmove
swap r> + swap repeat
r> drop nip u ;
\ example use
s" ώщыē" xreverse type \ outputs "ēыщώ"</syntaxhighlight>
=={{header|Fortran}}==
{{works with|Fortran|90 and later}}
<
CHARACTER(80) :: str = "This is a string"
Line 493 ⟶ 1,788:
WRITE(*,*) str
END PROGRAM Example</
{{out}}
This is a string
gnirts a si sihT
Another implementation that uses a recursive not-in-place algorithm:
<
implicit none
Line 522 ⟶ 1,817:
end function reverse
end program reverse_string</
{{out}}
<
no devil lived on</
Another shorter implementation (adapted version from stackoverflow question 10605574 how-to-reverse-a-chain-of-character-fortran-90):
<syntaxhighlight lang="fortran"> program reverse_string
implicit none
character (80) :: cadena
integer :: k, n
!
cadena = "abcdefgh"
n = len_trim (cadena)
!
write (*,*) cadena
forall (k=1:n) cadena (k:k) = cadena (n-k+1:n-k+1)
write (*,*) cadena
!
end program reverse_string</syntaxhighlight>
{{out}}
<pre>
abcdefgh
hgfedcba </pre>
=={{header|FreeBASIC}}==
<syntaxhighlight lang="freebasic">' FB 1.05.0 Win64
Function ReverseString(s As Const String) As String
If s = "" Then Return s
Dim length As Integer = Len(s)
Dim r As String = Space(length)
For i As Integer = 0 To length - 1
r[i] = s[length - 1 - i]
Next
Return r
End Function
Dim s As String = "asdf"
Print "'"; s; "' reversed is '"; ReverseString(s); "'"</syntaxhighlight>
{{out}}
<pre>
'asdf' reversed is 'fdsa'
</pre>
=={{header|Frink}}==
The built-in <CODE>reverse</CODE> function reverses a string or the elements of a list.
Frink's built-in <CODE>reverse[''string'']</CODE> is quite smart and uses a grapheme-based algorithm to handle Unicode correctly. That is, it preserves "user-perceived characters" that may consist of characters, combining accents, high-plane Unicode characters (that is, above U+FFFF,) surrogate pairs, ''etc.'' correctly.
Many languages will not work correctly with upper-plane Unicode characters because they are represented as Unicode "surrogate pairs" which are represented as two characters in a UTF-16 stream.
For example, the string "g\u0308o" represents a g with combining diaeresis, followed by the letter o. Or, in other words, "g̈o". Note that while there are three Unicode codepoints, only two "graphemes" are displayed. Using Frink's smart "reverse" function preserves these combined graphemes. A naive reverse would move the diaeresis over the o instead of the g.
<syntaxhighlight lang="frink">println[reverse["abcdef"]]</syntaxhighlight>
=={{header|Futhark}}==
Futhark has no real strings beyond a little bit of syntactic sugar, so this is the same as reversing an array.
<syntaxhighlight lang="futhark">
fun main(s: []i32) = s[::-1]
</syntaxhighlight>
=={{header|FutureBasic}}==
<syntaxhighlight lang="futurebasic">void local fn DoIt
CFStringRef s1 = @"asdf", s2 = @""
long index
for index = len(s1) - 1 to 0 step -1
s2 = fn StringByAppendingString( s2, mid(s1,index,1) )
next
print s1,s2
end fn
window 1
fn DoIt
HandleEvents</syntaxhighlight>
Output:<pre>
asdf fdsa</pre>
=={{header|Gambas}}==
'''[https://gambas-playground.proko.eu/?gist=e32989a1ffdc4428075ca6d4cb15dfa6 Click this link to run this code]'''
<syntaxhighlight lang="gambas">Public Sub Main()
Dim sString As String = "asdf"
Dim sOutput As String
Dim siCount As Short
For siCount = Len(sString) DownTo 1
sOutput &= Mid(sString, siCount, 1)
Next
Print sOutput
End</syntaxhighlight>
Output:
<pre>
fdsa
</pre>
=={{header|GAP}}==
<
# "fedcba"</
=={{header|Gema}}==
Reverse each line in the input stream. Using built in function:
<
Not using built in function (recursively apply substring to same rule):
<
=={{header|Genie}}==
Pretty sure the output capture fails the extra credit, but that may be more local setup and font installs rather than the glib functions used.
<syntaxhighlight lang="genie">[indent=4]
/*
Reverse a string, in Genie
valac reverse.gs
*/
init
utf8:string = "asdf"
combining:string = "asdf̅"
print utf8
print utf8.reverse()
print combining
print combining.reverse()</syntaxhighlight>
{{out}}
<pre>
prompt$ valac reverse.gs
prompt$ ./reverse
asdf
fdsa
as?df?
?fd?sa</pre>
=={{header|GFA Basic}}==
<syntaxhighlight lang="text">
PRINT @reverse$("asdf")
'
FUNCTION reverse$(string$)
LOCAL result$,i%
result$=""
FOR i%=1 TO LEN(string$)
result$=MID$(string$,i%,1)+result$
NEXT i%
RETURN result$
ENDFUNC
</syntaxhighlight>
=={{header|Go}}==
Functions below assume UTF-8 encoding. (The task mentions Unicode but does not specify an encoding.) Strings in Go are not restricted to be UTF-8, but Go has good support for it and works with UTF-8 most natually. As shown below, certain string conversions work in UTF-8 and the range clause over a string works in UTF-8. Go also has a Unicode package in the standard library that
<
import (
"fmt"
"unicode"
"unicode/utf8"
)
Line 560 ⟶ 1,990:
}
// reverseCodePoints interprets its argument as UTF-8 and ignores bytes
// that do not form valid UTF-8. return value is UTF-8.
func reverseCodePoints(s string) string {
r := make([]
start := len(s)
for _, c := range s {
start--
r[start] = c
}
}
return string(r[start:])
}
// reversePreservingCombiningCharacters interprets its argument as UTF-8
// and ignores bytes that do not form valid UTF-8. return value is UTF-8.
func reversePreservingCombiningCharacters(s string) string {
if s == "" {
return ""
}
p := []
r := make([]
start := len(r)
for i := 0; i < len(p); {
// quietly skip invalid UTF-8
if p[i] == utf8.RuneError {
i++
continue
}
j := i + 1
for j < len(p) && (unicode.Is(unicode.Mn, p[j]) ||
Line 584 ⟶ 2,025:
j++
}
for k :=
start--
r[
}
i = j
}
return (string(r[start:]))
}
Line 602 ⟶ 2,043:
r := reverseBytes(s)
fmt.Println("reversed bytes:", []byte(r), r)
fmt.Println("original code points:", []
r = reverseCodePoints(s)
fmt.Println("reversed code points:", []
r = reversePreservingCombiningCharacters(s)
fmt.Println("combining characters:", []
}</
{{out}}
<pre>
original: [97 115 100 102] asdf
Line 624 ⟶ 2,065:
=={{header|Groovy}}==
=====Solution:=====
<
{{out}}
<pre>.ablE was I ere' ,I saw elbA</pre>
=====Extra Credit:=====
<syntaxhighlight lang="groovy">def string = "as⃝df̅"
List combiningBlocks = [
Character.UnicodeBlock.COMBINING_DIACRITICAL_MARKS,
Character.UnicodeBlock.COMBINING_DIACRITICAL_MARKS_SUPPLEMENT,
Character.UnicodeBlock.COMBINING_HALF_MARKS,
Character.UnicodeBlock.COMBINING_MARKS_FOR_SYMBOLS
]
List chars = string as List
chars[1..-1].eachWithIndex { ch, i ->
if (Character.UnicodeBlock.of((char)ch) in combiningBlocks) {
chars[i..(i+1)] = chars[(i+1)..i]
}
}
println chars.reverse().join()</syntaxhighlight>
{{out}}
<pre>f̅ds⃝a</pre>
=={{header|Harbour}}==
<syntaxhighlight lang="visualfoxpro">FUNCTION Reverse( sIn )
LOCAL cOut := "", i
FOR i := Len( sIn ) TO 1 STEP -1
cOut += Substr( sIn, i, 1 )
NEXT
RETURN cOut</syntaxhighlight>
=={{header|Haskell}}==
<
This function as defined in the Haskell Prelude.
Though variants using a helper function with an additional accumulator argument are more efficient, and are now used by default in GHC.List unless the USE_REPORT_PRELUDE key is set.
Perhaps, for example:
<syntaxhighlight lang="haskell">accumulatingReverse :: [a] -> [a]
accumulatingReverse lst =
let rev xs a = foldl (flip (:)) a xs
in rev lst []</syntaxhighlight>
===Supporting combining characters===
<
import Data.List (groupBy)
myReverse = concat . reverse . groupBy (const isMark)</
<code>groupBy (const isMark)</code> is an unusual way of splitting a string into its combined characters
=={{header|HicEst}}==
<
L = LEN( string )
Line 650 ⟶ 2,128:
ENDDO
WRITE(Messagebox, Name) string </
=={{header|Icon}} and {{header|Unicon}}==
<
s := \arglist[1] | "asdf"
write(s," <-> ", reverse(s)) # reverse is built-in
end</
=={{header|Io}}==
<
=={{
<syntaxhighlight lang="insitux">
(reverse "hello")
</syntaxhighlight>
=={{header|J}}==
Reverse (<tt>|.</tt>) reverses a list of items (of any shape or type).
<syntaxhighlight lang="j"> |.'asdf'
fdsa</syntaxhighlight>
Extra credit:
First, a function to determine whether a Unicode character is a combining character:
<
iscombining=. 2 | ranges&I.</
Then we need to box groups of letters and combining characters, reverse, and unbox. The boxing function can be carried out easily with dyad cut, which uses the indices of the ones on the right as the starting points for groups of characters. For clarity, its inverse will be defined as raze, which simply runs together the items inside boxes of its argument.
<
After this, the solution is just to reverse under the split transformation. This also takes place under J code to convert from Unicode to integers.
<
f̅ds⃝a</
=={{header|Java}}==
=== Reverse Unicode Codepoints ===
Reversing codepoints works in most cases when reversing single characters wherever they are encoded on multi-bytes or not. But this doesn't work for composed characters.
<syntaxhighlight lang="java">
String reversed = new StringBuilder("as⃝df̅").reverse().toString(); // fd⃝sa
String reversed = new StringBuffer("as⃝df̅").reverse().toString(); // fd⃝sa
</syntaxhighlight>
Alternately, you could use a for-loop with the same issue.
<syntaxhighlight lang="java">
String string = "as⃝df̅";
StringBuilder reversed = new StringBuilder();
for (int index = string.length() - 1; index >= 0; index--)
reversed.append(string.charAt(index));
reversed; // fd⃝sa
</syntaxhighlight>
=== Reverse Unicode Graphemes ===
A third-party solution is to use [https://mvnrepository.com/artifact/com.ibm.icu/icu4j ICU4J].
A native solution, since JDK 15, is to use <code>Pattern.compile( "\\X" )</code> from <code>java.util.regex</code> to parse grapemes.
Another native solution, since JDK 20, is to use <code>java.text.BreakIterator</code> class that now parse graphemes correctly<ref>https://bugs.openjdk.org/browse/JDK-8291660</ref>.
<syntaxhighlight lang="java">
import java.text.BreakIterator;
public class Reverse {
/* works with Java 20+ only
* cf. https://bugs.openjdk.org/browse/JDK-8291660
*/
public static StringBuilder graphemeReverse(String text) {
BreakIterator boundary = BreakIterator.getCharacterInstance();
boundary.setText(text);
StringBuilder reversed = new StringBuilder();
int end = boundary.last();
int start = boundary.previous();
while (start != BreakIterator.DONE) {
reversed.append(text.substring(start, end));
end = start;
start = boundary.previous();
}
return reversed;
}
public static void main(String[] args) throws Exception {
String a = "as⃝df̅";
System.out.println(graphemeReverse(a)); // f̅ds⃝a
}
}
</syntaxhighlight>
=={{header|JavaScript}}==
=== Unicode ===
==== Split code points ====
<code><nowiki>split('')</nowiki></code> (with empty string argument) works only for ASCII. For Unicode strings, one of the two following methods can be used.
<syntaxhighlight lang="javascript">
example = 'Tux 🐧 penguin';
// array expansion operator
[...example].reverse().join('') // 'niugnep 🐧 xuT'
// split regexp separator with Unicode mode
example.split(/(?:)/u).reverse().join('') // 'niugnep 🐧 xuT'
// do not use
example.split('').reverse().join(''); // 'niugnep \udc27\ud83d xuT'
</syntaxhighlight>
==== Split graphemes =====
More generally, one would want to combine characters such as joining emojis or diacritics to be handled properly so enumerating over graphemes is a must.
<syntaxhighlight lang="javascript">
a = "\u{1F466}\u{1F3FB}\u{1f44b}"; // '👦🏻👋'
// wrong behavior - ASCII sequences
a.split('').reverse().join(''); // '\udc4b🁦\ud83d'
// wrong behavior - Unicode code points
[...a].reverse().join(''); // '👋🏻👦'
a.split(/(?:)/u).reverse().join(''); // '👋🏻👦'
// correct behavior - Unicode graphemes
[...new Intl.Segmenter().segment(a)].map(x => x.segment).reverse().join('') // 👋👦🏻
</syntaxhighlight>
=== ASCII ===
==== ES5 ====
<syntaxhighlight lang="javascript">//using chained methods
function reverseStr(s) {
return s.split('').reverse().join('');
}
//fast method using for loop
function reverseStr(s) {
for (var i = s.length - 1, o = ''; i >= 0; o += s[i--]) { }
return o;
}
//fast method using while loop (faster with long strings in some browsers when compared with for loop)
function reverseStr(s) {
var i = s.length, o = '';
while (i--) o += s[i];
return o;
}</syntaxhighlight>
==== ES6 ====
<syntaxhighlight lang="javascript">(() => {
// .reduceRight() can be useful when reversals
// are composed with some other process
let reverse1 = s => Array.from(s)
.reduceRight((a, x) => a + (x !== ' ' ? x : ' <- '), ''),
// but ( join . reverse . split ) is faster for
// simple string reversals in isolation
reverse2 = s => s.split('').reverse().join('');
return [reverse1, reverse2]
.map(f => f("Some string to be reversed"));
})();</syntaxhighlight>
{{Out}}
<syntaxhighlight lang="javascript">["desrever <- eb <- ot <- gnirts <- emoS", "desrever eb ot gnirts emoS"]</syntaxhighlight>
=={{header|Joy}}==
<syntaxhighlight lang="joy">DEFINE reverse == "" [swons] fold.
"asdf" reverse putchars.</syntaxhighlight>
{{out}}
<pre>fdsa</pre>
=={{header|jq}}==
jq's explode/implode filters are based on codepoints, and therefore "reverse_string" as defined here will reverse the sequence of codepoints.
The topic of Unicode combining characters is a large one that is not touched on here.
<syntaxhighlight lang="jq">def reverse_string: explode | reverse | implode;</syntaxhighlight>
'''Examples''':
"nöel" | reverse_string # => "leön"
"as⃝df̅" | reverse_string # => "̅fd⃝sa"
=={{header|Jsish}}==
ECMAScript has no builtin string reversal, so split the characters into an array, reverse the array and join it back together.
Jsi only supports UTF-8 literals so far (in release 2.8), character by character manipulation routines of multibyte UTF-8 data will not be correct. No extra credit, ''yet''.
<syntaxhighlight lang="javascript">var str = "Never odd or even";
puts(str);
puts(str.split('').reverse().join(''));</syntaxhighlight>
{{out}}
<pre>Never odd or even
neve ro ddo reveN</pre>
=={{header|Julia}}==
<syntaxhighlight lang="julia">julia> reverse("hey")
"yeh"</syntaxhighlight>
The <code>reverse</code> function reverses codepoints ([https://github.com/JuliaLang/julia/issues/6165 because this is the right behavior] for the main application of string reversal: reversed string processing by external C libraries). However, [https://github.com/JuliaLang/julia/pull/9261 starting in Julia 0.4], you can also reverse the graphemes if you want (i.e. to reverse "visual order" including combining characters etc.) by:
<syntaxhighlight lang="julia">julia> join(reverse(collect(graphemes("as⃝df̅"))))
"f̅ds⃝a"</syntaxhighlight>
=={{header|K}}==
Monadic reverse (| ) verb reverses a string or list of any shape
<syntaxhighlight lang="k">
|"asdf"
"fdsa"
| 23 4 5 1
1 5 4 23
</syntaxhighlight>
=={{header|Kotlin}}==
<syntaxhighlight lang="kotlin">fun main(args: Array<String>) {
println("asdf".reversed())
}</syntaxhighlight>
=={{header|L++}}==
<syntaxhighlight lang="lisp">(include "string" "algorithm")
(main
(decl std::string s)
(std::getline std::cin s)
(std::reverse (s.begin) (s.end))
(prn s))</syntaxhighlight>
=={{header|LabVIEW}}==
{{VI solution|LabVIEW_Reverse_a_string.png}}
=={{header|Lambdatalk}}==
<syntaxhighlight lang="scheme">
{S.reverse hello brave new world}
-> world new brave hello
</syntaxhighlight>
=={{header|Lang}}==
<syntaxhighlight lang="lang">
# Inv operator
fn.println(parser.op(-asdf))
# Ouput: fdsa
# Inv operator function
fn.println(fn.inv(asdf))
# Ouput: fdsa
</syntaxhighlight>
=={{header|Lang5}}==
<syntaxhighlight lang="lang5">: flip "" split reverse "" join ;
"qwer asdf" flip .</syntaxhighlight>
=={{header|langur}}==
The reverse() function will reverse a string according to graphemes.
<syntaxhighlight lang="langur">writeln reverse "don't you know"</syntaxhighlight>
{{out}}
<pre>wonk uoy t'nod</pre>
=={{header|Lasso}}==
<syntaxhighlight lang="lasso">local(input) = 'asdf'
#input->reverse</syntaxhighlight>
===Using Query Expression & Array===
More verbose than the string->reverse method, but this example illustrates different techniques to achieve the same result:
using string->values to iterate over a string in order, inserting at position 1, and joining the resulting array as a string.
<syntaxhighlight lang="lasso">local(input = 'asdf', output = array)
with i in #input->values
do #output->insertFirst(#i)
#output->join</syntaxhighlight>
=={{header|LC3 Assembly}}==
A string is stored as a zero-terminated array of character codes. To reverse it, we first scan forwards until we find the end; we then move backwards again, copying each code into a block of memory we have reserved for the purpose; and finally, when we have got back to the beginning, we append a terminal zero to the new string we have created. We can then call <tt>PUTS</tt> to print it.
<syntaxhighlight lang="lc3asm"> .ORIG 0x3000
LEA R1,STRING
LEA R2,GNIRTS
LD R3,MINUS1
NOT R5,R1
ADD R5,R5,1
SCAN LDR R4,R1,0
BRZ COPY
ADD R1,R1,1
BRNZP SCAN
COPY ADD R1,R1,R3
ADD R4,R1,R5
BRN COPIED
LDR R4,R1,0
STR R4,R2,0
ADD R2,R2,1
BRNZP COPY
COPIED AND R4,R4,0
STR R4,R2,0
LEA R0,GNIRTS
PUTS
HALT
MINUS1 .FILL 0xFFFF
STRING .STRINGZ "If thou beest he -- but O how fall'n! how chang'd"
GNIRTS .BLKW 128
.END</syntaxhighlight>
{{out}}
<pre>d'gnahc woh !n'llaf woh O tub -- eh tseeb uoht fI</pre>
=={{header|LFE}}==
Ordinary string:
<syntaxhighlight lang="lisp">
> (lists:reverse "asdf")
"fdsa"
</syntaxhighlight>
Create a UTF-8 encoded string:
<syntaxhighlight lang="lisp">
> (set encoded (binary ("åäö ð" utf8)))
#B(195 165 195 164 195 182 32 195 176)
</syntaxhighlight>
Display it, to be sure:
<syntaxhighlight lang="lisp">
> (io:format "~tp~n" (list encoded))
<<"åäö ð"/utf8>>
</syntaxhighlight>
Reverse it:
<syntaxhighlight lang="lisp">
> (lists:reverse (unicode:characters_to_list encoded))
"ð öäå"
</syntaxhighlight>
=={{header|Liberty BASIC}}==
{{works with|Just BASIC}}
{{works with|Run BASIC}}
<syntaxhighlight lang="lb">input$ ="abcdefgABCDEFG012345"
print input$
print ReversedStr$( input$)
Line 700 ⟶ 2,479:
ReversedStr$ =ReversedStr$ +mid$( in$, i, 1)
next i
end function</
=={{header|Lingo}}==
Lingo strings are always UTF-8 encoded and string operations are based on Unicode code points, so the "extra credit" is built-in:
<syntaxhighlight lang="lingo">on reverse (str)
res = ""
repeat with i = str.length down to 1
put str.char[i] after res
end repeat
return res
end</syntaxhighlight>
To reverse a string byte-wise, the ByteArray data type has to be used:
<syntaxhighlight lang="lingo">on reverseBytes (str)
ba = byteArray(str)
res = byteArray()
repeat with i = ba.length down to 1
res[res.length+1] = ba[i]
end repeat
return res
end</syntaxhighlight>
=={{header|LiveCode}}==
<syntaxhighlight lang="livecode">function reverseString S
repeat with i = length(S) down to 1
put char i of S after R
end repeat
return R
end reverseString</syntaxhighlight>
=={{header|LLVM}}==
<syntaxhighlight lang="llvm">; This is not strictly LLVM, as it uses the C library function "printf".
; LLVM does not provide a way to print values, so the alternative would be
; to just load the string into memory, and that would be boring.
; Additional comments have been inserted, as well as changes made from the output produced by clang such as putting more meaningful labels for the jumps
$"main.printf" = comdat any
@main.str = private unnamed_addr constant [12 x i8] c"Hello world\00", align 1
@"main.printf" = linkonce_odr unnamed_addr constant [4 x i8] c"%s\0A\00", comdat, align 1
define void @reverse(i64, i8*) {
%3 = alloca i8*, align 8 ; allocate str (local)
%4 = alloca i64, align 8 ; allocate len (local)
%5 = alloca i64, align 8 ; allocate i
%6 = alloca i64, align 8 ; allocate j
%7 = alloca i8, align 1 ; allocate t
store i8* %1, i8** %3, align 8 ; set str (local) to the parameter str
store i64 %0, i64* %4, align 8 ; set len (local) to the paremeter len
store i64 0, i64* %5, align 8 ; i = 0
%8 = load i64, i64* %4, align 8 ; load len
%9 = sub i64 %8, 1 ; decrement len
store i64 %9, i64* %6, align 8 ; j =
br label %loop
loop:
%10 = load i64, i64* %5, align 8 ; load i
%11 = load i64, i64* %6, align 8 ; load j
%12 = icmp ult i64 %10, %11 ; i < j
br i1 %12, label %loop_body, label %exit
loop_body:
%13 = load i8*, i8** %3, align 8 ; load str
%14 = load i64, i64* %5, align 8 ; load i
%15 = getelementptr inbounds i8, i8* %13, i64 %14 ; address of str[i]
%16 = load i8, i8* %15, align 1 ; load str[i]
store i8 %16, i8* %7, align 1 ; t = str[i]
%17 = load i64, i64* %6, align 8 ; load j
%18 = getelementptr inbounds i8, i8* %13, i64 %17 ; address of str[j]
%19 = load i8, i8* %18, align 1 ; load str[j]
%20 = getelementptr inbounds i8, i8* %13, i64 %14 ; address of str[i]
store i8 %19, i8* %20, align 1 ; str[i] = str[j]
%21 = load i8, i8* %7, align 1 ; load t
%22 = getelementptr inbounds i8, i8* %13, i64 %17 ; address of str[j]
store i8 %21, i8* %22, align 1 ; str[j] = t
;-- loop increment
%23 = load i64, i64* %5, align 8 ; load i
%24 = add i64 %23, 1 ; increment i
store i64 %24, i64* %5, align 8 ; store i
%25 = load i64, i64* %6, align 8 ; load j
%26 = add i64 %25, -1 ; decrement j
store i64 %26, i64* %6, align 8 ; store j
br label %loop
exit:
ret void
}
define i32 @main() {
;-- char str[]
%1 = alloca [12 x i8], align 1
;-- memcpy(str, "Hello world")
%2 = bitcast [12 x i8]* %1 to i8*
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8* getelementptr inbounds ([12 x i8], [12 x i8]* @main.str, i32 0, i32 0), i64 12, i32 1, i1 false)
;-- printf("%s\n", str)
%3 = getelementptr inbounds [12 x i8], [12 x i8]* %1, i32 0, i32 0
%4 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @"main.printf", i32 0, i32 0), i8* %3)
;-- %7 = strlen(str)
%5 = getelementptr inbounds [12 x i8], [12 x i8]* %1, i32 0, i32 0
%6 = call i64 @strlen(i8* %5)
;-- reverse(%6, str)
call void @reverse(i64 %6, i8* %5)
;-- printf("%s\n", str)
%7 = getelementptr inbounds [12 x i8], [12 x i8]* %1, i32 0, i32 0
%8 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @"main.printf", i32 0, i32 0), i8* %7)
;-- end of main
ret i32 0
}
;--- The declaration for the external C printf function.
declare i32 @printf(i8*, ...)
; Function Attrs: argmemonly nounwind
declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i32, i1)
declare i64 @strlen(i8*)</syntaxhighlight>
{{out}}
<pre>Hello world
dlrow olleH</pre>
=={{header|Logo}}==
REVERSE works on both words and lists.
<
=={{header|Lua}}==
Built-in string.reverse(s) or s:reverse().
=== ASCII ===
<syntaxhighlight lang="lua">
example = 'asdf'
string.reverse(example) -- fdsa
example:reverse() -- fdsa
</syntaxhighlight>
=== Unicode ===
Lua doesn't support Unicode strings.
=={{header|M2000 Interpreter}}==
===Using Custom Function===
Version 2, using insert to string (with no copies of strings)
<syntaxhighlight lang="m2000 interpreter">
Module ReverseString {
a$="as⃝df̅"
Print Len(a$), len.disp(a$)
Let i=1, j=Len(a$)
z$=String$(" ",j)
j++
do {
k$=mid$(a$, i, 1)
if i<len(a$) then {
while len.disp(k$+mid$(a$, i+1,1)) =len.disp(k$) {
k$+=mid$(a$, i+1,1)
i++
if i>len(a$) then exit
j--
}
j--
insert j, len(k$) Z$=K$
} else j-- :Insert j,1 z$=k$
if i>=len(a$) then exit
i++
} Always
Print len(z$), len.disp(z$)
Print z$="f̅ds⃝a"
Print z$
}
ReverseString
</syntaxhighlight>
===using StrRev$()===
this function (new to 9.5 version) use StrReverse from Vb6
<syntaxhighlight lang="m2000 interpreter">
a$="as⃝df̅"
b$=strrev$(a$)
clipboard b$
Print b$="̅fd⃝sa"
</syntaxhighlight>
=={{header|M4}}==
<
=={{header|
<syntaxhighlight lang="lisp">(readlist (reverse (explode "my-string")))</syntaxhighlight>
Output:
<pre>"gnirts-ym"</pre>
=={{header|MACRO-11}}==
<syntaxhighlight lang="macro11"> .TITLE REVERS
.MCALL .GTLIN,.PRINT,.EXIT
REVERS::.GTLIN #1$ ; READ STRING
MOV #1$,R0
JSR PC,REV ; REVERSE IT
.PRINT #1$ ; PRINT RESULT
.EXIT
1$: .BLKB 200
; REVERSE STRING AT R0
REV: MOV R0,R1
1$: TSTB (R1)+ ; FIND END OF STRING
BNE 1$
DEC R1 ; MOVE BACK TO LAST CHAR
2$: MOVB -(R1),R2 ; SWAP CHARS
MOVB (R0),(R1)
MOVB R2,(R0)+
CMP R0,R1 ; STOP WHEN POINTERS MEET
BLT 2$
RTS PC
.END REVERS</syntaxhighlight>
{{out}}
<pre>.revers
A man, a plan, a canal: Panama
amanaP :lanac a ,nalp a ,nam A</pre>
=={{header|Maple}}==
<syntaxhighlight lang="maple">> StringTools:-Reverse( "foo" );
"oof"</syntaxhighlight>
=={{header|Mathematica}}/{{header|Wolfram Language}}==
<syntaxhighlight lang="mathematica">StringReverse["asdf"]</syntaxhighlight>
=={{header|MATLAB}}==
Line 720 ⟶ 2,707:
Sample Usage:
<
'Grabbed her hand out the club and I said let''s skate.'])
ans =
.etaks s'tel dias I dna bulc eht tuo dnah reh debbarG .taerg dias I dna hsilgnE ekops ehs taht em dlot ehS</syntaxhighlight>
=={{header|Maxima}}==
<syntaxhighlight lang="maxima">sreverse("abcdef"); /* "fedcba" */
sreverse("rats live on no evil star"); /* not a bug :o) */</syntaxhighlight>
=={{header|MAXScript}}==
<
(
local reversed = ""
for i in s.count to 1 by -1 do reversed += s[i]
reversed
)</
=={{header|min}}==
{{works with|min|0.19.3}}
<syntaxhighlight lang="min">("" split reverse "" join) :reverse-str</syntaxhighlight>
=={{header|MiniScript}}==
<syntaxhighlight lang="miniscript">str = "This is a string"
print "Forward: " + str
newStr = ""
for i in range(str.len-1, 0)
newStr = newStr + str[i]
end for
print "Reversed: " + newStr</syntaxhighlight>
{{out}}
<pre>
Forward: This is a string
Reversed: gnirts a si sihT
</pre>
=={{header|MIPS Assembly}}==
<syntaxhighlight lang="mips">
# First, it gets the length of the original string
# Then, it allocates memory from the copy
# Then it copies the pointer to the original string, and adds the strlen
# subtract 1, then that new pointer is at the last char.
# while(strlen)
# copy char
# decrement strlen
# decrement source pointer
# increment target pointer
.text
strcpy:
addi $sp, $sp, -4
sw $s0, 0($sp)
add $s0, $zero, $zero
L1:
add $t1, $s0, $a1
lb $t2, 0($t1)
add $t3, $s0, $a0
sb $t2, 0($t3)
beq $t2, $zero, L2
addi $s0, $s0, 1
j L1
L2:
lw $s0, 0($sp)
addi $sp, $sp, 4
jr $ra
.data
ex_msg_og: .asciiz "Original string:\n"
ex_msg_cpy: .asciiz "\nCopied string:\n"
string: .asciiz "Nice string you got there!\n"
</syntaxhighlight>
=={{header|Mirah}}==
<
StringBuilder.new(s).reverse
end
puts reverse('reversed')</
=={{header|Miranda}}==
<syntaxhighlight lang="miranda">main :: [sys_message]
main = [Stdout (reverse "esreveR"),
Stdout "\n"]</syntaxhighlight>
{{out}}
<pre>Reverse</pre>
=={{header|Modula-2}}==
<syntaxhighlight lang="modula2">MODULE ReverseStr;
FROM FormatString IMPORT FormatString;
FROM Terminal IMPORT Write,WriteString,WriteLn,ReadChar;
PROCEDURE WriteInt(n : INTEGER);
VAR buf : ARRAY[0..15] OF CHAR;
BEGIN
FormatString("%i", buf, n);
WriteString(buf)
END WriteInt;
PROCEDURE ReverseStr(in : ARRAY OF CHAR; VAR out : ARRAY OF CHAR);
VAR ip,op : INTEGER;
BEGIN
ip := 0;
op := 0;
WHILE in[ip] # 0C DO
INC(ip)
END;
DEC(ip);
WHILE ip>=0 DO
out[op] := in[ip];
INC(op);
DEC(ip)
END
END ReverseStr;
TYPE A = ARRAY[0..63] OF CHAR;
VAR is,os : A;
BEGIN
is := "Hello World";
ReverseStr(is, os);
WriteString(is);
WriteLn;
WriteString(os);
WriteLn;
ReadChar
END ReverseStr.</syntaxhighlight>
=={{header|Modula-3}}==
<
IMPORT IO, Text;
Line 759 ⟶ 2,857:
BEGIN
IO.Put(String("Foobarbaz") & "\n");
END Reverse.</
{{out}}
<pre>
zabrabooF
Line 766 ⟶ 2,864:
=={{header|MUMPS}}==
<syntaxhighlight lang="mumps">REVERSE
;Take in a string and reverse it using the built in function $REVERSE
NEW S
READ:30 "Enter a string: ",S
WRITE !,$REVERSE(S)
QUIT</syntaxhighlight>
{{out}}
USER>D REVERSE^ROSETTA
Enter a string: Hello, World!
!dlroW ,olleH
</pre>
=={{header|Nanoquery}}==
<syntaxhighlight lang="nanoquery">def reverse(string)
l = ""
for char in list(str(string)).reverse()
l += char
end
return l
end</syntaxhighlight>
=={{header|Neko}}==
No extra credit for UTF in this example.
<syntaxhighlight lang="actionscript">/* Reverse a string, in Neko */
var reverse = function(s) {
var len = $ssize(s)
if len < 2 return s
var reverse = $smake(len)
var pos = 0
while len > 0 $sset(reverse, pos ++= 1, $sget(s, len -= 1))
return reverse
}
var str = "never odd or even"
$print(str, "\n")
$print(reverse(str), "\n\n")
str = "abcdefghijklmnopqrstuvwxyz"
$print(str, "\n")
$print(reverse(str), "\n\n")
$print("single test\n")
str = "a"
$print(str, "\n")
$print(reverse(str), "\n\n")
$print("empty test\n")
str = ""
$print(str, "\n")
$print(reverse(str), "\n")</syntaxhighlight>
{{out}}
<pre>prompt$ nekoc reverse.neko
prompt$ neko reverse.n
never odd or even
neve ro ddo reven
abcdefghijklmnopqrstuvwxyz
zyxwvutsrqponmlkjihgfedcba
single test
a
a
empty test
</pre>
Line 783 ⟶ 2,940:
===Supporting Combining Characters===
Compile with:<pre>ncc -reference:System.Windows.Forms reverse.n</pre>
<
using System.Globalization;
using System.Windows.Forms;
Line 805 ⟶ 2,962:
MessageBox.Show($"$test --> $(UReverse(test))"); //for whatever reason my console didn't display Unicode properly, but a MessageBox worked
}
}</
===Basic Reverse===
Doesn't require the '''System.Globalization''' namespace, probably a little less overhead.
<
{
mutable output = [];
Line 814 ⟶ 2,971:
output ::= c.ToString();
Concat("", output)
}</
=={{header|NetRexx}}==
<syntaxhighlight lang="netrexx">/* NetRexx */
options replace format comments java crossref savelog symbols nobinary
reverseThis = 'asdf'
sihTesrever = reverseThis.reverse
say reverseThis
say sihTesrever
return</syntaxhighlight>
{{out}}
<pre>
asdf
fdsa
</pre>
=={{header|NewLISP}}==
<syntaxhighlight lang="newlisp">(reverse "!dlroW olleH")</syntaxhighlight>
=={{header|Nial}}==
<
=fdsa</
=={{header|Nim}}==
=== Unicode codepoints ===
Since Nim 0.11.0, the <code>unicode</code> module provides a [https://nim-lang.github.io/Nim/unicode.html#reversed%2Cstring <code>reversed</code>] proc...
Hence:
<syntaxhighlight lang="nim">
import unicode
doAssert "foobar".reversed == "raboof"
doAssert "先秦兩漢".reversed == "漢兩秦先"
</syntaxhighlight>
This proc is enumerating codepoints so it will work with Unicode multi-bytes characters. A special handling was added so it's supports composing as well but since it's not enumerating graphemes it won't work with joining.
=== Unicode graphemes ===
There is no native method to handle grapheme currently.
=={{header|NS-HUBASIC}}==
<syntaxhighlight lang="ns-hubasic">10 STRING$="THIS TEXT IS REVERSED."
20 REVERSED$=""
30 FOR I=1 TO LEN(STRING$)
40 REVERSED$=MID$(STRING$,I,1)+REVERSED$
50 NEXT
60 PRINT REVERSED$</syntaxhighlight>
=={{header|Oberon-2}}==
Tested with [https://miasap.se/obnc OBNC].
<syntaxhighlight lang="oberon">MODULE reverse;
IMPORT Out, Strings;
VAR s: ARRAY 12 + 1 OF CHAR;
PROCEDURE Swap(VAR c, d: CHAR);
VAR oldC: CHAR;
BEGIN
oldC := c; c := d; d := oldC
END Swap;
PROCEDURE Reverse(VAR s: ARRAY OF CHAR);
VAR len, i: INTEGER;
BEGIN
len := Strings.Length(s);
FOR i := 0 TO len DIV 2 DO
Swap(s[i], s[len - 1 - i])
END
END Reverse;
BEGIN
s := "hello, world";
Reverse(s);
Out.String(s);
Out.Ln
END reverse.</syntaxhighlight>
=={{header|Objeck}}==
<
result := "asdf"->Reverse();
</syntaxhighlight>
=={{header|Objective-C}}==
This extends the <code>NSString</code> object adding a <code>reverseString</code> class method.
<syntaxhighlight lang="objc">#import <Foundation/Foundation.h>
@interface NSString (Extended)
Line 848 ⟶ 3,083:
return rtr;
}
@end</
Usage example:
<syntaxhighlight lang="objc">int main()
{
@autoreleasepool {
NSString *test = [@"!A string to be reverted!" reverseString];
NSLog(@"%@", test);
return 0;
}</
===Supporting combining characters===
Extra credit
<syntaxhighlight lang="objc">#import <Foundation/Foundation.h>
@interface NSString (Extended)
Line 886 ⟶ 3,117:
return ostr;
}
@end</
Usage example:
<syntaxhighlight lang="objc">int main()
{
@autoreleasepool {
NSString *test = [@"as⃝df̅" reverseString];
NSLog(@"%@", test);
return 0;
}</
=={{header|OCaml}}==
Since OCaml 4.02 we can use the handy [http://caml.inria.fr/pub/docs/manual-ocaml/libref/String.html#VALinit String.init] function.
Here a version that returns a new allocated string (preserving the original one):
{{works with|OCaml|4.02+}}
<syntaxhighlight lang="ocaml">let string_rev s =
let
let () =
print_endline (string_rev "Hello world!")</syntaxhighlight>
for in place modification we can't use strings anymore because strings became immutable in ocaml 4.02, so the type bytes has to be used instead:
<syntaxhighlight lang="ocaml">let rev_bytes bs =
let last = Bytes.length bs - 1 in
for i = 0 to last / 2 do
let j = last - i in
let c =
done
let () =
let s = Bytes.of_string "Hello World" in
rev_bytes s;
print_bytes s;
print_newline ();
;;</syntaxhighlight>
Here is a 100% functionnal string reversing function:
<syntaxhighlight lang="ocaml">let rec revs_aux strin list index =
if List.length list = String.length strin
then String.concat "" list
else
let revs s = revs_aux s [] 0
let () =
print_endline (revs "Hello World!")</syntaxhighlight>
will return "!dlroW olleH"
=={{header|Octave}}==
<
rev = s(length(s):-1:1)</
=={{header|Oforth}}==
<syntaxhighlight lang="oforth">reverse</syntaxhighlight>
=={{header|Ol}}==
<syntaxhighlight lang="scheme">
(define (rev s)
(runes->string (reverse (string->runes s))))
; testing:
(print (rev "Hello, λ!"))
; ==> !λ ,olleH
</syntaxhighlight>
=={{header|OOC}}==
<syntaxhighlight lang="ooc">
main: func {
"asdf" reverse() println() // prints "fdsa"
}
</syntaxhighlight>
=={{header|OpenEdge/Progress}}==
<syntaxhighlight lang
INPUT i_c AS CHARACTER
):
Line 956 ⟶ 3,215:
END FUNCTION.
MESSAGE reverseString( "asdf" ) VIEW-AS ALERT-BOX.</syntaxhighlight>
=={{header|OxygenBasic}}==
<syntaxhighlight lang="oxygenbasic">
'8 BIT CHARACTERS
string s="qwertyuiop"
sys a,b,i,j,le=len s
'
for i=1 to le
j=le-i+1
if j<=i then exit for
a=asc s,i
b=asc s,j
mid s,j,chr a
mid s,i,chr b
next
'
print s
'16 BIT CHARACTERS
wstring s="qwertyuiop"
sys a,b,i,j,le=len s
'
for i=1 to le
j=le-i+1
if j<=i then exit for
a=unic s,i
b=unic s,j
mid s,j,wchr a
mid s,i,wchr b
next
'
print s
</syntaxhighlight>
==OxygenBasic x86 Assembler==
32 bit code, 8-bit characters:
<syntaxhighlight lang="oxygenbasic">
string s="qwertyuiop"
sys p=strptr s, le=len s
mov esi,p
mov edi,esi
add edi,le
dec edi
(
cmp esi,edi
jge exit
mov al,[esi]
mov ah,[edi]
mov [esi],ah
mov [edi],al
inc esi
dec edi
repeat
)
print s
</syntaxhighlight>
=={{header|Oz}}==
Strings are lists. A function "Reverse" defined on lists is part of the implementation.
<
An efficient (tail-recursive) implementation could look like this:
<
fun {DoReverse Xs Ys}
case Xs of nil then Ys
Line 972 ⟶ 3,291:
in
fun {Reverse Xs} {DoReverse Xs nil} end
end</
Oz uses a single-byte encoding by default. If you decide to use a multi-byte encoding, Reverse will not work correctly.
=={{header|PARI/GP}}==
===Version #1.===
<syntaxhighlight lang="parigp">reverse(s)=concat(Vecrev(s))</syntaxhighlight>
===Version #2.===
{{Works with|PARI/GP|2.7.4 and above}}
<syntaxhighlight lang="parigp">
\\ Return reversed string str.
\\ 3/3/2016 aev
sreverse(str)={return(Strchr(Vecrev(Vecsmall(str))))}
{
\\ TEST1
print(" *** Testing sreverse from Version #2:");
print(sreverse("ABCDEF"));
my(s,sr,n=10000000);
s="ABCDEFGHIJKL";
for(i=1,n, sr=sreverse(s));
}
</syntaxhighlight>
{{Output}}
<pre>
*** Testing sreverse from Version #2:
FEDCBA
(17:28) gp > ##
*** last result computed in 8,642 ms.
</pre>
<syntaxhighlight lang="parigp">
\\ Version #1 upgraded to complete function. Practically the same.
reverse(str)={return(concat(Vecrev(str)))}
{
\\ TEST2
print(" *** Testing reverse from Version #1:");
print(reverse("ABCDEF"));
my(s,sr,n=10000000);
s="ABCDEFGHIJKL";
for(i=1,n, sr=reverse(s));
}
</syntaxhighlight>
{{Output}}
<pre>
*** Testing reverse from Version #1:
FEDCBA
(17:31) gp > ##
*** last result computed in 11,814 ms.
</pre>
=={{header|Pascal}}==
Line 987 ⟶ 3,353:
Standard Pascal doesn't have a separate string type, but uses arrays of char for strings. Note that Standard Pascal doesn't allow a return type of char array, therefore the destination array is passed through a var parameter (which is more efficient anyway).
<
procedure reverse(s: array[min .. max: integer] of char, var result: array[min1 .. max1: integer] of char);
var
Line 995 ⟶ 3,361:
for i := 0 to len-1 do
result[min1 + len-1 - i] := s[min + i]
end;</
<syntaxhighlight lang="pascal">{Copy and paste it in your program}
function revstr(my_s:string):string;
var out_s:string;
Line 1,006 ⟶ 3,371:
out_s:=out_s+my_s[ls-i+1];
revstr:=out_s;
end;</syntaxhighlight>
=== Extended Pascal, Turbo Pascal, Delphi and compatible compilers ===
<
var i:integer;
var tmp:char;
Line 1,021 ⟶ 3,384:
reverse:=s;
end;
end;</
alternative as procedure which changes the original
<syntaxhighlight lang="pascal">procedure revString(var s:string);
var
i,j:integer;
tmp:char;
begin
i := 1;
j := length(s);
while i<j do
begin
tmp:=s[i];
s[i]:=s[j];
s[j]:=tmp;
inc(i);
dec(j)
end;
end;</syntaxhighlight>
=={{header|Peloton}}==
Padded out, variable length Chinese dialect
<syntaxhighlight lang="sgml"><# 显示 指定 变量 反转顺序 字串>集装箱|猫坐在垫子</#></syntaxhighlight>
This assigns the reverse of 'the cat sat on the mat' to the variable 'container' and displays the result which is <pre>子垫在坐猫</pre> which Google Translate renders as <pre>Sub-pad sitting cat</pre>.
The same again but with everything in Korean.
<syntaxhighlight lang="sgml"><# 보이십 할당하 변물건 열거꾸 문자그>컨테이너|고양이가 매트 위에 앉아</#></syntaxhighlight>
Reversing the Korean makes an untranslatable-by-Google mess of the sentence, viz <pre>아앉 에위 트매 가이양고</pre>.
The short-opcode version in English dialect is
<syntaxhighlight lang="sgml"><@ SAYLETVARREVLIT>集装箱|猫坐在垫子</@></syntaxhighlight>
Peloton works in Unicode.
=={{header|Perl}}==
[https://perldoc.perl.org/functions/reverse reverse()] works in the context of a List or a scalar, not a string.
<syntaxhighlight lang="perl">use utf8;
binmode STDOUT, ":utf8";
# to reverse characters (code points):
# to reverse graphemes:
print join("", reverse "José" =~ /\X/g), "\n";
$string = 'ℵΑΩ 駱駝道 🤔 🇸🇧 🇺🇸 🇬🇧 👨👩👧👦🆗🗺';
print join("", reverse $string =~ /\X/g), "\n";</syntaxhighlight>
{{out}}
<pre>rosiv
ésoJ
🗺🆗👨👩👧👦 🇬🇧 🇺🇸 🇸🇧 🤔 道駝駱 ΩΑℵ</pre>
=={{header|Pharo}}==
<syntaxhighlight lang="pharo">'123' reversed</syntaxhighlight>
=={{header|Phix}}==
<!--<syntaxhighlight lang="phix">(phixonline)-->
<span style="color: #0000FF;">?</span><span style="color: #7060A8;">reverse</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"asdf"</span><span style="color: #0000FF;">)</span>
<!--</syntaxhighlight>-->
However that would go horribly wrong on utf8 strings, even without combining characters, so... this seems ok on "as\u203Ddf\u0305", as long as it is displayed in a message box rather than a Windows Console (even with chcp 65001 and Lucida Console, the characters do not combine). It actually works better under pwa/p2js than on desktop/Phix, you can find a copy of this code in demo/HelloUTF8.exw which outputs the result in a message box and therefore looks much better on the latter.<br>
Note that [[XXXX_redacted#Phix]] adds some ZERO-WIDTH-JOINER handling to the inner code.
<!--<syntaxhighlight lang="phix">(phixonline)-->
<span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">unicode_reverse</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">utf8</span><span style="color: #0000FF;">)</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">utf32</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">utf8_to_utf32</span><span style="color: #0000FF;">(</span><span style="color: #000000;">utf8</span><span style="color: #0000FF;">)</span>
<span style="color: #000080;font-style:italic;">-- The assumption is made that <char><comb1><comb2>
-- and <char><comb2><comb1> etc would work the same.
-- The following loop converts <char><comb1><comb2>
-- to <comb1><comb2><char>, as a pre-reverse() step.</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">utf32</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">ch</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">utf32</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">]</span>
<span style="color: #008080;">if</span> <span style="color: #0000FF;">(</span><span style="color: #000000;">ch</span><span style="color: #0000FF;">>=</span><span style="color: #000000;">0x300</span> <span style="color: #008080;">and</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;"><=</span><span style="color: #000000;">0x36f</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">or</span> <span style="color: #0000FF;">(</span><span style="color: #000000;">ch</span><span style="color: #0000FF;">>=</span><span style="color: #000000;">0x1dc0</span> <span style="color: #008080;">and</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;"><=</span><span style="color: #000000;">0x1dff</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">or</span> <span style="color: #0000FF;">(</span><span style="color: #000000;">ch</span><span style="color: #0000FF;">>=</span><span style="color: #000000;">0x20d0</span> <span style="color: #008080;">and</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;"><=</span><span style="color: #000000;">0x20ff</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">or</span> <span style="color: #0000FF;">(</span><span style="color: #000000;">ch</span><span style="color: #0000FF;">>=</span><span style="color: #000000;">0xfe20</span> <span style="color: #008080;">and</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;"><=</span><span style="color: #000000;">0xfe2f</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">utf32</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">utf32</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">-</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span>
<span style="color: #000000;">utf32</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">-</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">ch</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #000000;">utf32</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">reverse</span><span style="color: #0000FF;">(</span><span style="color: #000000;">utf32</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">utf8</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">utf32_to_utf8</span><span style="color: #0000FF;">(</span><span style="color: #000000;">utf32</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">utf8</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #004080;">string</span> <span style="color: #000000;">r4</span> <span style="color: #0000FF;">=</span> <span style="color: #008000;">"as\u203Ddf\u0305"</span><span style="color: #0000FF;">,</span>
<span style="color: #000000;">rt</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">r4</span><span style="color: #0000FF;">&</span><span style="color: #008000;">" reversed is "</span><span style="color: #0000FF;">&</span><span style="color: #000000;">unicode_reverse</span><span style="color: #0000FF;">(</span><span style="color: #000000;">r4</span><span style="color: #0000FF;">)&</span><span style="color: #008000;">"\n"</span>
<span style="color: #7060A8;">puts</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #000000;">rt</span><span style="color: #0000FF;">)</span>
<!--</syntaxhighlight>-->
=={{header|PHP}}==
=== Unicode ===
==== Code points ====
If you want Unicode support, you have to use some multibyte function. Sadly, PHP doesn't contain <code>mb_strrev()</code>. One of functions which support Unicode and is useful in this case is <code>preg_split()</code>.
<syntaxhighlight lang="php">
// Will split every Unicode character to array, reverse array and will convert it to string.
join('', array_reverse(preg_split('""u', $string, -1, PREG_SPLIT_NO_EMPTY)));
</syntaxhighlight>
With PHP 7.4+ and 8+, it's also possible to use <code>mb_str_split()</code>, which may ends easier.
<syntaxhighlight lang="php">
implode('', array_reverse(mb_str_split($string)));
</syntaxhighlight>
==== Graphemes ====
When using combining characters such as diacritics or ZWJ (joining), reversing code points will mess with the result, reversing the graphemes instead is mandatory. This is generally the best and safest approach. As there is no <code>grapheme_reverse()</code> function or grapheme iterator, one has to implement it with <code>grapheme_strlen</code> and <code>grapheme_substr</code>. In PHP, there is no Unicode escape sequence so to specify characters by code point a tricks must be used: for example, using the escape sequence of HTML entities and then convert it to a Unicode encoding such as UTF-8.
<syntaxhighlight lang="php">
$a = mb_convert_encoding('👦🏻👋', 'UTF-8', 'HTML-ENTITIES'); // 👦🏻👋
function str_to_array($string)
{
$length = grapheme_strlen($string);
$ret = [];
for ($i = 0; $i < $length; $i += 1) {
$ret[] = grapheme_substr($string, $i, 1);
}
return $ret;
}
function utf8_strrev($string)
{
return implode(array_reverse(str_to_array($string)));
}
print_r(utf8_strrev($a)); // 👋👦🏻
</syntaxhighlight>
=== ASCII ===
<syntaxhighlight lang="php">strrev($string);</syntaxhighlight>
=={{header|PicoLisp}}==
<
{{out}}
<pre>-> "ßÜÖÄüöä"</pre>
=={{header|Pike}}==
For simple ASCII:
<syntaxhighlight lang="pike">reverse("foo");</syntaxhighlight>
{{out}}
<pre>"oof"</pre>
When dealing with Unicode (or any other supported encoding) care must
be taken primarily in the output step to serialize the Unicode string
into something the sink can handle. IO functions will throw an error
if sent raw wide strings.
<syntaxhighlight lang="pike">#charset utf8
void main()
{
string s = "ßÜÖÄüöää ἀρχῇ";
write("%s\n", string_to_utf8( reverse(s) ));
}</syntaxhighlight>
{{out}}
<pre>
ῇχρἀ ääöüÄÖÜß
</pre>
=={{header|PL/I}}==
<syntaxhighlight lang="pl/i">s = reverse(s);</syntaxhighlight>
=={{header|
<syntaxhighlight lang="plainenglish">To run:
Start up.
Put "asdf" into a string.
Reverse the string.
Shut down.</syntaxhighlight>
=={{header|plainTeX}}==
Works well if the string has no space (spaces are gobbled).
<syntaxhighlight lang="tex">\def\gobtoA#1\revA{}\def\gobtoB#1\revB{}
\def\reverse#1{\reversei{}#1\revA\revB\revB\revB\revB\revB\revB\revB\revB\revA}
\def\reversei#1#2#3#4#5#6#7#8#9{\gobtoB#9\revend\revB\reversei{#9#8#7#6#5#4#3#2#1}}
\def\revend\revB\reversei#1#2\revA{\gobtoA#1}
\reverse{Rosetta}
\bye</syntaxhighlight>
Output:
<pre>attesoR</pre>
=={{header|Pop11}}==
<syntaxhighlight lang="pop11">define reverse_string(s);
lvars i, l = length(s);
for i from l by -1 to 1 do
Line 1,056 ⟶ 3,580:
endfor;
consstring(l);
enddefine;</
=={{header|PostScript}}==
The following implementation works on arrays of numerics as well as characters ( string ).
<syntaxhighlight lang="postscript">/reverse{
/str exch def
/temp str 0 get def
Line 1,073 ⟶ 3,595:
}repeat
str pstack
}def</syntaxhighlight>
{{Out}}
<syntaxhighlight lang="postscript">[1 2 3] reverse % input
[3 2 1]
(Hello World) reverse % input
(dlroW olleH)</syntaxhighlight>
=={{header|PowerBASIC}}==
<syntaxhighlight lang="powerbasic">#DIM ALL
#COMPILER PBCC 6
FUNCTION PBMAIN () AS LONG
CON.PRINT STRREVERSE$("PowerBASIC")
END FUNCTION</syntaxhighlight>
=={{header|PowerShell}}==
=== For ASCII ===
Test string
<
====Array indexing====
Creating a character array from the end to the string's start and join it together into a string again.
{{works with|PowerShell|1}}
<
{{works with|PowerShell|2}}
<
{{works with|PowerShell|2}}
<syntaxhighlight lang
====Regular expressions====
Creating a regular expression substitution which captures every character of the string in a capture group and uses a reverse-ordered string of references to those to construct the reversed string.
{{works with|PowerShell|1}}
<
('(.)' * $s.Length),
[string]::Join('', ($s.Length..1 | ForEach-Object { "`$$_" }))</
{{works with|PowerShell|2}}
<
('(.)' * $s.Length),
-join ($s.Length..1 | ForEach-Object { "`$$_" } )</
{{works with|PowerShell|3}}
<syntaxhighlight lang="powershell">
[Regex]::Matches($s,'.','RightToLeft').Value -join ''
</syntaxhighlight>
=== For Unicode ===
==== For codepoints ====
Since PowerShell 7, there is a <code>EnumerateRunes()</code> method to enumerate Unicode codepoints. Enumerating codepoints works for multi-bytes characters but not for composing or joining.
<syntaxhighlight lang="powershell">
$a = 'abc 🐧 def'
$enum = $a.EnumerateRunes() | % { "$_" }
-join $enum[$enum.length..0] # fed 🐧 cba
</syntaxhighlight>
==== For graphemes ====
For composing or joining, enumerating graphemes is required.
<syntaxhighlight lang="powershell">
$a = "aeiou`u{0308}yz"
$enum = [System.Globalization.StringInfo]::GetTextElementEnumerator($a)
$arr = @()
while($enum.MoveNext()) { $arr += $enum.GetTextElement() }
[array]::reverse($arr)
$arr -join '' # zyüoiea
</syntaxhighlight>
=={{header|Prolog}}==
{{works with|SWI Prolog}}
<syntaxhighlight lang="prolog">reverse("abcd", L), string_to_list(S,L).</syntaxhighlight>
{{Out}}
<pre>
L = [100,99,98,97],
S = "dcba". </pre>
The main workings are hidden inside the reverse/2 predicate,
so lets write one to see how it works:
<syntaxhighlight lang="prolog">accRev([H|T], A, R) :- accRev(T, [H|A], R).
accRev([], A, A).
rev(L,R) :- accRev(L,[],R).</syntaxhighlight>
=={{header|PureBasic}}==
<
=={{header|Python}}==
===Optimized for user input===
<syntaxhighlight lang
===Already known string===
<syntaxhighlight lang
or
<syntaxhighlight lang="python">''.join(reversed(string))</syntaxhighlight>
===Python: Unicode reversal===
(See [http://paddy3118.blogspot.com/2009/07/case-of-disappearing-over-bar.html this article] for more information from which this is improved)
'''Note:''' How this looks may be subject to how the tool you are using to view this page can render Unicode.
<syntaxhighlight lang="python">import unicodedata
def ureverse(ustring):
'Reverse a string including unicode combining characters'
groupedchars = []
uchar = list(ustring)
while uchar:
if
groupedchars[-1] += uchar.pop(0)
else:
Line 1,172 ⟶ 3,709:
# Grouped reversal
groupedchars = groupedchars[::-1]
return ''.join(groupedchars)
def say_string(s):
return ' '.join([s, '=', ' | '.join(unicodedata.name(ch, '') for ch in s)])
def say_rev(s):
print(f"Input: {say_string(s)}")
print(f"Character reversed: {say_string(s[::-1])}")
print(f"Unicode reversed: {say_string(ureverse(s))}")
print(f"Unicode reverse²: {say_string(ureverse(ureverse(s)))}")
if __name__ == '__main__':
ucode = ''.join(
{{out}}
<pre>Input: Åström = LATIN CAPITAL LETTER A | COMBINING RING ABOVE | LATIN SMALL LETTER S | LATIN SMALL LETTER T | LATIN SMALL LETTER R | LATIN SMALL LETTER O | COMBINING DIAERESIS | LATIN SMALL LETTER M
Character reversed: m̈orts̊A = LATIN SMALL LETTER M | COMBINING DIAERESIS | LATIN SMALL LETTER O | LATIN SMALL LETTER R | LATIN SMALL LETTER T | LATIN SMALL LETTER S | COMBINING RING ABOVE | LATIN CAPITAL LETTER A
Unicode reversed: mörtsÅ = LATIN SMALL LETTER M | LATIN SMALL LETTER O | COMBINING DIAERESIS | LATIN SMALL LETTER R | LATIN SMALL LETTER T | LATIN SMALL LETTER S | LATIN CAPITAL LETTER A | COMBINING RING ABOVE
Unicode reverse²: Åström = LATIN CAPITAL LETTER A | COMBINING RING ABOVE | LATIN SMALL LETTER S | LATIN SMALL LETTER T | LATIN SMALL LETTER R | LATIN SMALL LETTER O | COMBINING DIAERESIS | LATIN SMALL LETTER M
</pre>
If this code is then used:
<syntaxhighlight lang="python">ucode = ''.join(chr(int(n[2:], 16)) for n in
'U+006B U+0301 U+0075 U+032D U+006F U+0304 U+0301 U+006E'.split())
say_rev(ucode)</syntaxhighlight>
It produces this output
{{out}}
<pre>Input: ḱṷṓn = LATIN SMALL LETTER K | COMBINING ACUTE ACCENT | LATIN SMALL LETTER U | COMBINING CIRCUMFLEX ACCENT BELOW | LATIN SMALL LETTER O | COMBINING MACRON | COMBINING ACUTE ACCENT | LATIN SMALL LETTER N
Character reversed: ń̄o̭úk = LATIN SMALL LETTER N | COMBINING ACUTE ACCENT | COMBINING MACRON | LATIN SMALL LETTER O | COMBINING CIRCUMFLEX ACCENT BELOW | LATIN SMALL LETTER U | COMBINING ACUTE ACCENT | LATIN SMALL LETTER K
Unicode reversed: nṓṷḱ = LATIN SMALL LETTER N | LATIN SMALL LETTER O | COMBINING MACRON | COMBINING ACUTE ACCENT | LATIN SMALL LETTER U | COMBINING CIRCUMFLEX ACCENT BELOW | LATIN SMALL LETTER K | COMBINING ACUTE ACCENT
Unicode reverse²: ḱṷṓn = LATIN SMALL LETTER K | COMBINING ACUTE ACCENT | LATIN SMALL LETTER U | COMBINING CIRCUMFLEX ACCENT BELOW | LATIN SMALL LETTER O | COMBINING MACRON | COMBINING ACUTE ACCENT | LATIN SMALL LETTER N</pre>
'''This uses the unicode string mentioned in the task:'''
<syntaxhighlight lang="python">ucode = ''.join(chr(int(n, 16))
for n in ['61', '73', '20dd', '64', '66', '305'])
say_rev(ucode)</syntaxhighlight>
It produces this output
{{out}}
<pre>Input: as⃝df̅ = LATIN SMALL LETTER A | LATIN SMALL LETTER S | COMBINING ENCLOSING CIRCLE | LATIN SMALL LETTER D | LATIN SMALL LETTER F | COMBINING OVERLINE
Character reversed: ̅fd⃝sa = COMBINING OVERLINE | LATIN SMALL LETTER F | LATIN SMALL LETTER D | COMBINING ENCLOSING CIRCLE | LATIN SMALL LETTER S | LATIN SMALL LETTER A
Unicode reversed: f̅d⃝sa = LATIN SMALL LETTER F | COMBINING OVERLINE | LATIN SMALL LETTER D | COMBINING ENCLOSING CIRCLE | LATIN SMALL LETTER S | LATIN SMALL LETTER A
Unicode reverse²: as⃝df̅ = LATIN SMALL LETTER A | LATIN SMALL LETTER S | COMBINING ENCLOSING CIRCLE | LATIN SMALL LETTER D | LATIN SMALL LETTER F | COMBINING OVERLINE</pre>
=={{header|Quackery}}==
reverse is predefined (and applies to nests in general, including strings) as:
<syntaxhighlight lang="quackery"> [ dup nest? if
[ [] swap witheach
[ nested
swap join ] ] ] is reverse ( x --> x )</syntaxhighlight>
=={{header|Qi}}==
It's simplest just to use the common lisp REVERSE function.
<syntaxhighlight lang="qi">(REVERSE "ABCD")</syntaxhighlight>
=={{header|R}}==
{{works with|R|2.8.1}}
The following code works with UTF-8 encoded strings too.
<
return(
paste(
Line 1,192 ⟶ 3,777:
,collapse="")
)
}</syntaxhighlight>
Alternatively (using rev() function):
<syntaxhighlight lang="r"> revstring <- function(s) paste(rev(strsplit(s,"")[[1]]),collapse="")</syntaxhighlight>
<syntaxhighlight lang="r">revstring("asdf")
revstring("m\u00f8\u00f8se")
Encoding("m\u00f8\u00f8se") # just to check if on your system it's something
# different!</
{{out}}
<pre>
[1] "fdsa"
Line 1,204 ⟶ 3,793:
[1] "UTF-8"
</pre>
R can encode strings in Latin1 and UTF-8 (the default may depend on the locale); the <tt>Encoding(string)</tt> can be used to know if the string is encoded in Latin1 or UTF-8; the encoding can be forced (<tt>Encoding(x) <- "latin1"</tt>), or we can use <tt>iconv</tt> to properly translate between encodings whenever possible.
=={{header|Racket}}==
As in Scheme:
<syntaxhighlight lang="racket">#lang racket
(define (string-reverse s)
(list->string (reverse (string->list s))))
(string-reverse "aoeu")</syntaxhighlight>
{{out}}
<pre>Welcome to DrRacket, version 5.3.3.5--2013-02-20(5eddac74/d) [3m].
Language: racket; memory limit: 512 MB.
"ueoa"
> </pre>
=={{header|Raku}}==
(formerly Perl 6)
{{Works with|rakudo|2018.08}}
Raku handles graphemes, multi-byte characters and emoji correctly by default.
<syntaxhighlight lang="raku" line>say "hello world".flip;
say "as⃝df̅".flip;
say 'ℵΑΩ 駱駝道 🤔 🇸🇧 🇺🇸 🇬🇧 👨👩👧👦🆗🗺'.flip;</syntaxhighlight>
{{out}}
<pre>dlrow olleh
f̅ds⃝a
🗺🆗👨👩👧👦 🇬🇧 🇺🇸 🇸🇧 🤔 道駝駱 ΩΑℵ</pre>
=={{header|RapidQ}}==
<syntaxhighlight lang="vb">
print reverse$("This is a test")
</syntaxhighlight>
=={{header|Rascal}}==
<syntaxhighlight lang="rascal">import String;
reverse("string")</syntaxhighlight>
=={{header|Raven}}==
<syntaxhighlight lang="raven">"asdf" reverse</syntaxhighlight>
{{out}}
<pre>fdsa</pre>
=={{header|REBOL}}==
<syntaxhighlight lang="rebol">print reverse "asdf"</syntaxhighlight>
Note the string is reversed in place. If you were using it anywhere else, you would find it reversed:
<syntaxhighlight lang="rebol">x: "asdf"
print reverse x
print x ; Now reversed.</syntaxhighlight>
REBOL/View 2.7.6.3.1 14-Mar-2008 does not handle Unicode strings. This is planned for REBOL 3.
=={{header|
<syntaxhighlight lang="red">>> reverse "asdf"
== "fdsa"</syntaxhighlight>
=={{header|Refal}}==
<syntaxhighlight lang="refal">$ENTRY Go {
= <Prout <Reverse 'asdf'>>;
};
Reverse {
(e.X) = e.X;
(e.X) s.C e.Y = <Reverse (s.C e.X) e.Y>;
e.X = <Reverse () e.X>;
};</syntaxhighlight>
{{out}}
<pre>fdsa</pre>
=={{header|ReScript}}==
<syntaxhighlight lang="rescript">let rev_string = (s) => {
let len = Js.String2.length(s)
let arr = []
for i in 0 to (len-1) {
let c = Js.String2.get(s, len - 1 - i)
let _ = Js.Array2.push(arr, c)
}
Js.String2.concatMany("", arr)
}
Js.log(rev_string("abcdefg"))</syntaxhighlight>
{{out}}
<pre>
$ bsc revstr.res > revstr.bs.js
$ node revstr.bs.js
gfedcba
</pre>
=={{header|Retro}}==
<syntaxhighlight lang="retro">'asdf s:reverse s:put</syntaxhighlight>
=={{header|REXX}}==
All methods shown below also work with '''NULL''' values (strings with a zero length).
===using REVERSE BIF===
<syntaxhighlight lang="rexx">/*REXX program to reverse a string (and show before and after strings).*/
string1 = 'A man, a plan, a canal, Panama!'
string2 = reverse(string1)
say ' original string: ' string1
say ' reversed string: ' string2
/*stick a fork in it, we're done.*/</syntaxhighlight>
'''output'''
<pre>
original string: A man, a plan, a canal, Panama!
reversed string: !amanaP ,lanac a ,nalp a ,nam A
</pre>
===using SUBSTR BIF, left to right===
<syntaxhighlight lang="rexx">/*REXX program to reverse a string (and show before and after strings).*/
string1 = 'A man, a plan, a canal, Panama!'
string2 =
do j=1 for length(string1)
string2 = substr(string1,j,1)string2
end /*j*/
say ' original string: ' string1
say ' reversed string: ' string2
/*stick a fork in it, we're done.*/</syntaxhighlight>
'''output''' is identical to the 1<sup>st</sup> REXX version.
<br><br>(Regarding the previous example) Another method of coding an abutment (an implied concatenation) is:
<syntaxhighlight lang="rexx"> string2 = substr(string1,j,1) || string2
/*───── or ─────*/
string2= substr(string1,j,1)string2</syntaxhighlight>
===using SUBSTR BIF, right to left===
<syntaxhighlight lang="rexx">/*REXX program to reverse a string (and show before and after strings).*/
string1 = 'A man, a plan, a canal, Panama!'
string2 =
do j=length(string1) to 1 by -1
string2 = string2 || substr(string1,j,1)
end /*j*/
say ' original string: ' string1
say ' reversed string: ' string2
/*stick a fork in it, we're done.*/</syntaxhighlight>
'''output''' is identical to the 1<sup>st</sup> version.
<br><br>
=={{header|Ring}}==
<syntaxhighlight lang="ring">
cStr = "asdf" cStr2 = ""
for x = len(cStr) to 1 step -1 cStr2 += cStr[x] next
See cStr2 # fdsa
</syntaxhighlight>
=={{header|RLaB}}==
<syntaxhighlight lang="rlab">>> x = "rosettacode"
rosettacode
Line 1,256 ⟶ 3,952:
>> rx
edocattesor</syntaxhighlight>
=={{header|Robotic}}==
<syntaxhighlight lang="robotic">
. "local1 = Main string"
. "local2 = Temporary string storage"
. "local3 = String length"
set "$local1" to ""
set "$local2 " to ""
set "local3" to 0
input string "String to reverse:"
set "$local1" to "&INPUT&"
set "$local2" to "$local1"
set "local3" to "$local2.length"
loop start
set "$local1.(('local3' - 1) - 'loopcount')" to "$local2.('loopcount')"
loop for "('local3' - 1)"
* "Reversed string: &$local1& (Length: &$local1.length&)"
end
</syntaxhighlight>
=={{header|RPL}}==
{{works with|Halcyon Calc|4.2.7}}
≪ ""
OVER SIZE 1 '''FOR''' j
OVER j DUP SUB +
-1 '''STEP''' SWAP DROP
≫ '<span style="color:blue">RVSTR</span>' STO
"ABC" <span style="color:blue">RVSTR</span>
{{out}}
<pre>1: "CBA"</pre>
=={{header|Ruby}}==
<
reversed = str.reverse
"résumé niño".reverse #=> "oñin émusér"</syntaxhighlight>
for extra credit
<syntaxhighlight lang="ruby">
graphemes = 'as⃝df̅'.scan(/\X/)
reversed = graphemes.reverse
graphemes.join #=> "f̅ds⃝a"
</syntaxhighlight>
=={{header|Run BASIC}}==
{{works with|Just BASIC}}
{{works with|Liberty BASIC}}
{{works with|QBasic}}
{{works with|Yabasic}}
<syntaxhighlight lang="runbasic">string$ = "123456789abcdefghijk"
for i = len(string$) to 1 step -1
print mid$(string$,i,1);
next i</syntaxhighlight>
=={{header|Rust}}==
Reversing ASCII byte-slice (in-place):
<syntaxhighlight lang="rust">let mut buffer = b"abcdef".to_vec();
buffer.reverse();
assert_eq!(buffer, b"fedcba");</syntaxhighlight>
Reversing Unicode scalar values:
<syntaxhighlight lang="rust">let output: String = "一二三四五六七八九十".chars().rev().collect();
assert_eq!(output, "十九八七六五四三二一");</syntaxhighlight>
Reversing a <code>Chars</code> iterator doesn't solve the complete problem, because it iterates unicode scalar values, which doesn't account for combining marks:
<syntaxhighlight lang="rust">let output: String = "as⃝df̅".chars().rev().collect();
assert_ne!(output, "f̅ds⃝a"); // should be this
assert_eq!(output, "̅fd⃝sa");</syntaxhighlight>
Reversing graphemes clusters, which is provided by the [https://unicode-rs.github.io/unicode-segmentation/unicode_segmentation/struct.Graphemes.html unicode-segmentation] crate, solves the problem:
<syntaxhighlight lang="rust">use unicode_segmentation::UnicodeSegmentation;
let output: String = "as⃝df̅".graphemes(true).rev().collect();
assert_eq!(output, "f̅ds⃝a");</syntaxhighlight>
=={{header|S-lang}}==
Here is an 8-bit version:
<syntaxhighlight lang="s-lang">variable sa = "Hello, World", aa = Char_Type[strlen(sa)+1];
init_char_array(aa, sa);
array_reverse(aa);
% print(aa);
% Unfortunately, strjoin() only joins strings, so we map char()
% [sadly named: actually converts char into single-length string]
% onto the array:
print( strjoin(array_map(String_Type, &char, aa), "") );</syntaxhighlight>
Output: "dlroW ,olleH"
For a Unicode version, we'll create a variant of init_char_array().
Side note: If needed, strbytelen() would give total length of string.
<syntaxhighlight lang="s-lang">define init_unicode_array(a, buf)
{
variable len = strbytelen(buf), ch, p0 = 0, p1 = 0;
while (p1 < len) {
(p1, ch) = strskipchar(buf, p1, 1);
if (ch < 0) print("oops.");
a[p0] = ch;
p0++;
}
}
variable su = "Σὲ γνωρίζω ἀπὸ τὴν κόψη";
variable au = Int_Type[strlen(su)+1];
init_unicode_array(au, su);
array_reverse(au);
% print(au);
print(strjoin(array_map(String_Type, &char, au), "") );</syntaxhighlight>
Output: "ηψόκ νὴτ ὸπἀ ωζίρωνγ ὲΣ"
Note: The init...array() functions include the terminating '\0' chars, but
we don't have to filter them out as char(0) produces a zero-length string.
=={{header|SAS}}==
<syntaxhighlight lang="sas">data _null_;
length a b $11;
a="I am Legend";
b=reverse(a);
put a;
put b;
run;</syntaxhighlight>
=={{header|Sather}}==
<
main is
s ::= "asdf";
Line 1,273 ⟶ 4,090:
-- current implementation does not handle multibyte encodings correctly
end;
end;</
=={{header|Scala}}==
Easy way:
<syntaxhighlight lang="scala">"asdf".reverse</syntaxhighlight>
Slightly less easy way:
<syntaxhighlight lang="scala">"asdf".foldRight("")((a,b) => b+a)</syntaxhighlight>
Unicode-aware
<syntaxhighlight lang="scala">def reverse(s: String) = {
import java.text.{Normalizer,BreakIterator}
val norm = Normalizer.normalize(s, Normalizer.Form.NFKC) // waffle -> waffle (optional)
val it = BreakIterator.getCharacterInstance
it setText norm
def break(it: BreakIterator, prev: Int, result: List[String] = Nil): List[String] = it.next match {
case BreakIterator.DONE => result
case cur => break(it, cur, norm.substring(prev, cur) :: result)
}
break(it, it.first).mkString
}</syntaxhighlight>
{{out}}
<pre>scala> reverse("as⃝df̅")
res0: String = f̅ds⃝a</pre>
Unicode-aware, method 2: I can't guarantee it get all the cases, but it does work with combining characters as well as supplementary characters. I did not bother to preserve the order of newline characters, and I didn't even consider directionality beyond just ruling it out.
<syntaxhighlight lang="scala">def reverseString(s: String) = {
import java.lang.Character._
Line 1,314 ⟶ 4,146:
}
recurse(splitString(s), Nil)
}</
REPL on Windows doesn't handle Unicode, so I'll show the bytes instead:
<pre>
scala> res71 map ("\\u%04x" format _.toInt)
Line 1,327 ⟶ 4,157:
=={{header|Scheme}}==
<
(list->string (reverse (string->list s))))</
> (string-reverse "asdf")
"fdsa"
=={{header|Scratch}}==
[[File:ScratchReverseAString.png]]
=={{header|Sed}}==
<
/../! b
Line 1,351 ⟶ 4,184:
# Remove the newline markers
s/\n//g</syntaxhighlight>
=={{header|Seed7}}==
Seed7 strings are encoded with UTF-32 therefore no special Unicode solution is necessary. The following demonstrates one way of reversing a string with a user-defined function.
<syntaxhighlight lang="ada" line="1">$ include "seed7_05.s7i";
const func string: reverso(in string: stri) is func
result
var string: result is "";
Line 1,374 ⟶ 4,203:
const proc: main is func
begin
writeln(
end func;</syntaxhighlight>The following demonstrates the use of the built-in 'reverse' function:<syntaxhighlight lang="ada" line="1">
$ include "seed7_05.s7i";
const proc: main is func
begin
writeln(reverse("Was it a cat I saw?"));
end func;
</syntaxhighlight>{{out}}
<pre>
was I tac a ti saW
</pre>
=={{header|Self}}==
In-place reversal:
<syntaxhighlight lang="self">'asdf' copyMutable reverse</syntaxhighlight>
=={{header|SenseTalk}}==
<syntaxhighlight lang="sensetalk">put "asdf" reversed -- reverse on the fly
set imp to "rumpelstiltskin"
reverse imp -- reverse in place
put imp
</syntaxhighlight>
{{out}}
<pre>
fdsa
nikstlitslepmur
</pre>
=={{header|SequenceL}}==
'''Using Library Function:'''
There is a library function to reverse any Sequence. This works for strings since strings are Sequences of characters.
<syntaxhighlight lang="sequencel">import <Utilities/Sequence.sl>;
main(args(2)) := Sequence::reverse(args[1]);</syntaxhighlight>
'''The Library Function:'''
The following is the library implementation of the reverse function.
<syntaxhighlight lang="sequencel">reverse<T> : T(1) -> T(1);
reverse(list(1))[i] :=
let
range := - ((1 ... size(list)) - (size(list) + 1));
in
list[i] foreach i within range;</syntaxhighlight>
=={{header|Sidef}}==
<syntaxhighlight lang="ruby">"asdf".reverse; # fdsa
"résumé niño".reverse; # oñin émusér</syntaxhighlight>
=={{header|Simula}}==
<syntaxhighlight lang="simula">
BEGIN
TEXT PROCEDURE REV(S); TEXT S;
BEGIN
TEXT T;
INTEGER L,R;
T :- COPY(S);
L := 1; R := T.LENGTH;
WHILE L < R DO
BEGIN
CHARACTER CL,CR;
T.SETPOS(L); CL := T.GETCHAR;
T.SETPOS(R); CR := T.GETCHAR;
T.SETPOS(L); T.PUTCHAR(CR);
T.SETPOS(R); T.PUTCHAR(CL);
L := L+1;
R := R-1;
END;
REV :- T;
END REV;
TEXT INP;
INP :- "asdf";
OUTTEXT(INP); OUTIMAGE;
OUTTEXT(REV(INP)); OUTIMAGE;
END
</syntaxhighlight>
{{out}}
<pre>
asdf
fdsa
</pre>
=={{header|Slate}}==
In-place reversal:
<syntaxhighlight lang
Non-destructive reversal:
<syntaxhighlight lang
=={{header|Smalltalk}}==
<syntaxhighlight lang
{{works with|Smalltalk/X}}
the above does inplace, destructive reverse. It is usually better to use
<syntaxhighlight lang="smalltalk">'asdf' reversed</syntaxhighlight>
which returns a new string.
=={{header|SNOBOL4}}==
ASCII-only
<
end</
{{out}}
<pre>reverse</pre>
=={{header|Standard ML}}==
<
val string = "asdf";
val reversed = str_reverse string;</
=={{header|Stata}}==
Use '''[https://www.stata.com/help.cgi?f_strreverse strreverse]''' if there are only ASCII characters, and '''[https://www.stata.com/help.cgi?f_ustrreverse ustrreverse]''' if there are Unicode characters in the string.
<syntaxhighlight lang="stata">. scalar s="ARS LONGA VITA BREVIS"
. di strreverse(s)
SIVERB ATIV AGNOL SRA
. scalar s="Ἐν ἀρχῇ ἐποίησεν ὁ θεὸς τὸν οὐρανὸν καὶ τὴν γῆν"
. di ustrreverse(s)
νῆγ νὴτ ὶακ νὸναρὐο νὸτ ςὸεθ ὁ νεσηίοπἐ ῇχρἀ νἘ</syntaxhighlight>
=={{header|Stringle}}==
This inputs a string from the user and outputs its reverse. The <code>\</code> ''reverse'' operator reverses any string.
<syntaxhighlight lang="stringle">$ \$</syntaxhighlight>
=={{header|Swift}}==
Swift's strings are iterated by <code>Character</code>s, which represent "Unicode grapheme clusters", so reversing it reverses it with combining characters too:
{{works with|Swift|2.x+}}
<syntaxhighlight lang="swift">func reverseString(s: String) -> String {
return String(s.characters.reverse())
}
print(reverseString("asdf"))
print(reverseString("as⃝df̅"))</syntaxhighlight>
{{works with|Swift|1.x}}
<syntaxhighlight lang="swift">func reverseString(s: String) -> String {
return String(reverse(s))
}
println(reverseString("asdf"))
println(reverseString("as⃝df̅"))</syntaxhighlight>
{{out}}
<pre>
fdsa
f̅ds⃝a
</pre>
=={{header|Symsyn}}==
<syntaxhighlight lang="symsyn">
| reverse string
c : 'abcdefghijklmnopqrstuvwxyz'
d : ' '
c []
i
#c j
- j
if i < j
c.i d 1
c.j c.i 1
d c.j
- j
+ i
goif
endif
c []
</syntaxhighlight>
OR
<syntaxhighlight lang="symsyn">
c : 'abcdefghijklmnopqrstuvwxyz'
c []
$s
#c j
if j > 0
- j
+ c.j $s 1
goif
endif
$s []
</syntaxhighlight>
{{out}}
<pre>
abcdefghijklmnopqrstuvwxyz
zyxwvutsrqponmlkjihgfedcba
</pre>
=={{header|Tailspin}}==
<syntaxhighlight lang="tailspin">
templates reverse
'$:[ $... ] -> $(last..first:-1)...;' !
end reverse
'asdf' -> reverse -> !OUT::write
'
' -> !OUT::write
'as⃝df̅' -> reverse -> !OUT::write
</syntaxhighlight>
{{out}}
<pre>
fdsa
f̅ds⃝a
</pre>
=={{header|Tcl}}==
<
string reverse asdf</
=={{header|TI-83 BASIC}}==
Note: length( and sub( can be found in the catalog.
<
:For(I,1,length(Ans)-1
:sub(Ans,2I,1)+Ans
:End
:sub(
=={{header|TMG}}==
Unix TMG:
<syntaxhighlight lang="unixtmg">prog: parse(str);
str: smark any(!<<>>) scopy str/done = { 1 2 };
done: ;</syntaxhighlight>
=={{header|Tosh}}==
<syntaxhighlight lang="tosh">when flag clicked
ask "Say something..." and wait
set i to (length of answer)
set inv to ""
repeat until i = 0
set inv to (join (inv) (letter (i) of answer))
change i by -1
end
say inv</syntaxhighlight>
=={{header|Transd}}==
<syntaxhighlight lang="scheme">#lang transd
MainModule : {
_start: (lambda (with s "as⃝df̅"
(textout (reverse s))
// reversing user input
(textout "\nPlease, enter a string: ")
(textout "Input: " (reverse (read s)))
))
}</syntaxhighlight>
{{out}}
<pre>
̅fd⃝sa
Please, enter a string: Hello!
Input: !olleH
</pre>
=={{header|Turing}}==
Iterative solution, for character shovelers:
<syntaxhighlight lang="turing">function reverse (s : string) : string
var rs := ""
for i : 0 .. length (s) - 1
rs := rs + s (length (s) - i)
end for
result rs
end reverse
put reverse ("iterative example")
put reverse (reverse ("iterative example"))</syntaxhighlight>
{{out}}
<pre>
elpmaxe evitareti
iterative example
</pre>
Recursive solution, more natural in Turing:
<syntaxhighlight lang="turing">function reverse (s : string) : string
if s = "" then
result s
else
result reverse (s (2 .. *)) + s (1)
end if
end reverse
put reverse ("recursive example")
put reverse (reverse ("recursive example"))</syntaxhighlight>
{{out}}
<pre>
elpmaxe evisrucer
recursive example
</pre>
=={{header|TUSCRIPT}}==
<
SET input="was it really a big fat cat i saw"
SET reversetext=TURN (input)
PRINT "before: ",input
PRINT "after: ",reversetext</syntaxhighlight>
{{out}}
<pre>
before: was it really a big fat cat i saw
after: was i tac taf gib a yllaer ti saw
</pre>
=={{header|
<syntaxhighlight lang="bash">
#!/bin/bash
str=abcde
for((i=${#str}-1;i>=0;i--)); do rev="$rev${str:$i:1}"; done
echo $rev
</syntaxhighlight>
'''or'''
<syntaxhighlight lang="bash">
str='i43go1342iu 23iu4o 23iu14i324y 2i13'
rev <<< "$str"
#rev is not built-in function, though is in /usr/bin/rev
</syntaxhighlight>
=={{header|Unlambda}}==
Reverse the whole input:
<syntaxhighlight lang="unlambda">``@c`d``s`|k`@c</syntaxhighlight>
=={{header|Ursala}}==
<syntaxhighlight lang="ursala">#import std
#cast %s
Line 1,442 ⟶ 4,544:
example = ~&x 'asdf'
verbose_example = reverse 'asdf'</
{{out}}
<pre>
'fdsa'
</pre>
=={{header|Vala}}==
<syntaxhighlight lang="vala">int main (string[] args) {
if (args.length < 2) {
stdout.printf ("Please, input a string.\n");
return 0;
}
var str = new StringBuilder ();
for (var i = 1; i < args.length; i++) {
str.append (args[i] + " ");
}
stdout.printf ("%s\n", str.str.strip ().reverse ());
return 0;
}</syntaxhighlight>
=={{header|VBA}}==
===Non-recursive version===
<syntaxhighlight lang="vba">Public Function Reverse(aString as String) as String
' returns the reversed string
dim L as integer 'length of string
dim newString as string
newString = ""
L = len(aString)
for i = L to 1 step -1
newString = newString & mid$(aString, i, 1)
next
Reverse = newString
End Function</syntaxhighlight>
===Recursive version===
<syntaxhighlight lang="vba">Public Function RReverse(aString As String) As String
'returns the reversed string
'do it recursively: cut the string in two, reverse these fragments and put them back together in reverse order
Dim L As Integer 'length of string
Dim M As Integer 'cut point
L = Len(aString)
If L <= 1 Then 'no need to reverse
RReverse = aString
Else
M = Int(L / 2)
RReverse = RReverse(Right$(aString, L - M)) & RReverse(Left$(aString, M))
End If
End Function</syntaxhighlight>
===Example dialogue===
<pre>
print Reverse("Public Function Reverse(aString As String) As String")
gnirtS sA )gnirtS sA gnirtSa(esreveR noitcnuF cilbuP
print RReverse("Sunday Monday Tuesday Wednesday Thursday Friday Saturday Love")
evoL yadrutaS yadirF yadsruhT yadsendeW yadseuT yadnoM yadnuS
print RReverse(Reverse("I know what you did last summer"))
I know what you did last summer
</pre>
=={{header|VBScript}}==
{{works with|Windows Script Host|*}}
<syntaxhighlight lang="vbscript">
WScript.Echo StrReverse("asdf")
</syntaxhighlight>
=={{header|Vedit macro language}}==
This routine reads the text from current line, reverses it and stores the reversed string in text register 10:
<syntaxhighlight lang="vedit">Reg_Empty(10)
for (BOL; !At_EOL; Char) {
Reg_Copy_Block(10, CP, CP+1, INSERT)
}</
This routine reverses the current line in-place:
<syntaxhighlight lang="vedit">BOL
while (!At_EOL) {
Block_Copy(EOL_pos-1, EOL_pos, DELETE)
}</
=={{header|Visual Basic}}==
{{works with|Visual Basic|6}}
<syntaxhighlight lang="vb">Debug.Print VBA.StrReverse("Visual Basic")</syntaxhighlight>
=={{header|Visual Basic .NET}}==
'''Compiler:''' >= Visual Basic 2012
Includes both a simple version and a version that uses .NET's built-in ability to enumerate strings by grapheme to support combining characters.
Since the windows console may not support Unicode, the program can optionally redirect its output to a file.
<syntaxhighlight lang="vbnet">#Const REDIRECTOUT = True
Module Program
Const OUTPATH = "out.txt"
ReadOnly TestCases As String() = {"asdf", "as⃝df̅", "Les Misérables"}
' SIMPLE VERSION
Function Reverse(s As String) As String
Dim t = s.ToCharArray()
Array.Reverse(t)
Return New String(t)
End Function
' EXTRA CREDIT VERSION
Function ReverseElements(s As String) As String
' In .NET, a text element is series of code units that is displayed as one character, and so reversing the text
' elements of the string correctly handles combining character sequences and surrogate pairs.
Dim elements = Globalization.StringInfo.GetTextElementEnumerator(s)
Return String.Concat(AsEnumerable(elements).OfType(Of String).Reverse())
End Function
' Wraps an IEnumerator, allowing it to be used as an IEnumerable.
Iterator Function AsEnumerable(enumerator As IEnumerator) As IEnumerable
Do While enumerator.MoveNext()
Yield enumerator.Current
Loop
End Function
Sub Main()
Const INDENT = " "
#If REDIRECTOUT Then
Const OUTPATH = "out.txt"
Using s = IO.File.Open(OUTPATH, IO.FileMode.Create),
sw As New IO.StreamWriter(s)
Console.SetOut(sw)
#Else
Try
Console.OutputEncoding = Text.Encoding.ASCII
Console.OutputEncoding = Text.Encoding.UTF8
Console.OutputEncoding = Text.Encoding.Unicode
Catch ex As Exception
Console.WriteLine("Failed to set console encoding to Unicode." & vbLf)
End Try
#End If
For Each c In TestCases
Console.WriteLine(c)
Console.WriteLine(INDENT & "SIMPLE: " & Reverse(c))
Console.WriteLine(INDENT & "ELEMENTS: " & ReverseElements(c))
Console.WriteLine()
Next
#If REDIRECTOUT Then
End Using
#End If
End Sub
End Module</syntaxhighlight>
{{out|note=copied from Notepad}}
Output is presented using non-fixed-width typeface to properly display combining characters.
<pre style="font-family:TimesNewRoman,Times New Roman,Times,serif">asdf
SIMPLE: fdsa
ELEMENTS: fdsa
as⃝df̅
SIMPLE: ̅fd⃝sa
ELEMENTS: f̅ds⃝a
Les Misérables
SIMPLE: selbaŕesiM seL
ELEMENTS: selbarésiM seL</pre>
=={{header|Wart}}==
<syntaxhighlight lang="wart">(rev "asdf")</syntaxhighlight>
Wart doesn't support Unicode yet.
=={{header|V (Vlang)}}==
<syntaxhighlight lang="v (vlang)">const list =
('
Hello world!
你好世界！
Salamu, Dunia!
こんにちは世界！
¡Hola Mundo!
Chào thế giới!
Hallo Welt!
')
fn main() {
for line in list.split('\n') {if line !='' {println(reverse_string(line))}}
}
fn reverse_string(word string) string {
return word.runes().reverse().string()
}</syntaxhighlight>
{{out}}
<pre>
!dlrow olleH
！界世好你
!ainuD ,umalaS
！界世はちにんこ
!odnuM aloH¡
!iớig ếht oàhC
!tleW ollaH
</pre>
=={{header|Wren}}==
{{libheader|Wren-str}}
{{libheader|Wren-upc}}
<syntaxhighlight lang="wren">import "./str" for Str
import "./upc" for Graphemes
for (word in ["asdf", "josé", "møøse", "was it a car or a cat I saw", "😀🚂🦊"]) {
System.print(Str.reverse(word))
}
for (word in ["as⃝df̅", "ℵΑΩ 駱駝道 🤔 🇸🇧 🇺🇸 🇬🇧 👨👩👧👦🆗🗺"]) {
System.print(Graphemes.new(word).toList[-1..0].join())
}</syntaxhighlight>
{{out}}
<pre>
fdsa
ésoj
esøøm
was I tac a ro rac a ti saw
🦊🚂😀
f̅ds⃝a
🗺🆗👨👩👧👦 🇬🇧 🇺🇸 🇸🇧 🤔 道駝駱 ΩΑℵ
</pre>
=={{header|Wortel}}==
<syntaxhighlight lang="wortel">; the @rev operator reverses strings and arrays
@rev "abc" ; returns "cba"
; or the same thing using a pointer expression
!~r "abc"</syntaxhighlight>
=={{header|XBS}}==
Using the standard library
<syntaxhighlight lang="xbs">log(string.reverse("Hello"))</syntaxhighlight>
{{out}}
<pre>
olleH
</pre>
Using [[JavaScript]] methods
<syntaxhighlight lang="xbs">log("Hello"->split("")->reverse()->join(""));</syntaxhighlight>
{{out}}
<pre>
olleH
</pre>
Using a custom method
<syntaxhighlight lang="xbs">func ReverseString(String){
set Final = "";
for(i=?String-1;0;-1){
Final+=String[i];
}
send Final;
}
log(ReverseString("Hello"));</syntaxhighlight>
{{out}}
<pre>
elloH
</pre>
=={{header|XPL0}}==
<syntaxhighlight lang="xpl0">include c:\cxpl\codes; \intrinsic 'code' declarations
string 0; \use zero-terminated strings, instead of MSb terminated
func StrLen(Str); \Return the number of characters in an ASCIIZ string
char Str;
int I;
for I:= 0 to -1>>1-1 do
if Str(I) = 0 then return I;
func RevStr(S); \Reverse the order of the bytes in a string
char S;
int L, I, T;
[L:= StrLen(S);
for I:= 0 to L/2-1 do
[T:= S(I); S(I):= S(L-I-1); S(L-I-1):= T];
return S;
];
[Text(0, RevStr("a")); CrLf(0);
Text(0, RevStr("ab")); CrLf(0);
Text(0, RevStr("abc")); CrLf(0);
Text(0, RevStr("Able was I ere I saw Elba.")); CrLf(0);
]</syntaxhighlight>
Output:
<pre>
a
ba
cba
.ablE was I ere I saw elbA
</pre>
=={{header|Yorick}}==
This only handles ASCII characters. It works by converting a string to an array of char; dropping the last character (which is the null byte); reversing the order of the characters; then converting back to a string.
<
=={{header|Z80 Assembly}}==
This method uses the stack as a temporary store to reverse the order of characters in a string, and self-modifying code to restore the loop counter.
<syntaxhighlight lang="z80">PrintChar equ $BB5A ;Amstrad CPC bios call
Terminator equ 0 ;null terminator for strings
org $8000
ld hl, StringA
call ReverseString
ld hl, StringA
call PrintString
ret ;return to basic
StringA:
byte "12345678",0
;;;; SUBROUTINES
GetStringLength:
;HL = STRING. RETURNS LENGTH IN B. LENGTH IS ONE-INDEXED AND DOES NOT INCLUDE TERMINATOR.
ld b,0 ;clear B
loop_getStringLength:
ld a,(hl) ;read the next char
cp Terminator ;is it the terminator?
ret z ;if so, exit
inc hl ;point HL to next character
inc b ;increase tally
jr loop_getStringLength ;repeat
ReverseString:
;reverse the order of letters in a text string.
;e.g. "ABCD" -> "DCBA"
;the terminator stays put.
;INPUT: HL = SOURCE ADDRESS OF STRING
push de
push hl
push hl
call GetStringLength
pop hl
pop de ;LD DE,HL
LD a,b ;LOAD B INTO A
LD (SMC_ReverseString+1),a ;STORE IT LATER IN THE CODE SO WE CAN RETRIEVE IT.
; TO RECAP, BOTH HL AND DE POINT TO THE BEGINNING OF THE STRING WE WANT TO REVERSE. B EQUALS THE LENGTH OF THE STRING.
; B HAS BEEN BACKED UP WITHOUT USING THE STACK BY STORING IT AS THE OPERAND OF A LATER INSTRUCTION THAT LOADS B WITH A NUMERIC VALUE.
; PUSH BC WOULD NOT HAVE WORKED SINCE THE PROGRAM NEEDS TO PUSH EACH LETTER OF THE STRING DURING THE LOOP.
LOOP_REVERSESTRING_PUSH:
;start at the beginning of the string and push each letter in it, except the terminator.
ld a,(de)
push af
inc de
djnz LOOP_REVERSESTRING_PUSH
SMC_ReverseString:
ld b,$42 ;LETS US PRESERVE B WITHOUT PUSHING IT. THE $42 IS OVERWRITTEN WITH THE STRING'S LENGTH.
LOOP_REVERSESTRING_POP:
;Starting at the beginning of the string, pop A off the stack and store it into the string. This puts the letters back in the reverse
; order.
pop af
ld (hl),a
inc hl
djnz LOOP_REVERSESTRING_POP
pop de
ret</syntaxhighlight>
{{out}}
<pre>
87654321
</pre>
=={{header|zkl}}==
These only handle ASCII characters, no extra credit.
<pre>"this is a test".reverse()</pre>
Old school ways to do it:
Build by prepending characters, creates n strings:
<pre>"this is a test".reduce(fcn(p,c){c+p})</pre>
Convert to list, reverse, convert back to string:
<pre>"this is a test".split("").reverse().concat()</pre>
Write to a byte buffer and convert to string:
<pre>"this is a test".pump(Void,Data().insert.fp(0)).text</pre>
The ".fp(0)" creates a closure so each character is fed to data.insert(0,c). pump is a method that sends each character to a function to a sink (in this case /dev/null). The output is the result of the last call, which is data.insert which is self/data.
{{omit from|bc|no string operations}}
{{omit from|dc|no string operations}}
{{omit from|Openscad}}
[[Wikipedia::https://en.wikipedia.org/wiki/Comparison_of_programming_languages_%28string_functions%29#reverse]]
=={{header|Zoea}}==
<syntaxhighlight lang="zoea">
program: reverse_string
input: xyzzy
output: yzzyx
</syntaxhighlight>
=={{header|Zoea Visual
[http://zoea.co.uk/examples/zv-rc/Reverse_string.png Reverse string]
=={{header|Zig}}==
We can use `.*` to dereference a literal string pointer to an array, and use `std.mem.reverse` to reverse the slice of that array in-place:
<syntaxhighlight lang="zig">
var s = "socat".*;
std.mem.reverse(u8, &s);
</syntaxhighlight>
or:
<syntaxhighlight lang="zig">
var s = "socat".*;
std.mem.reverse(u8, s[0..]);
</syntaxhighlight>
String `s` now becomes `"tacos"`.
Tested on version 0.9.0. Reference: [https://ziglang.org/documentation/0.9.0/#String-Literals-and-Unicode-Code-Point-Literals].
| |||