Loops/While

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Revision as of 19:07, 10 September 2010 by rosettacode>Kbowley (Add Bash example)
Task
Loops/While
You are encouraged to solve this task according to the task description, using any language you may know.

Start an integer value at 1024. Loop while it is greater than 0. Print the value (with a newline) and divide it by two each time through the loop.

6502 Assembly

Code is called as a subroutine (i.e. JSR LoopsWhile). Specific OS/hardware routines for printing are left unimplemented. <lang 6502asm>LoopsWhile: PHA ;push accumulator onto stack

LDA #$00 ;the 6502 is an 8-bit processor STA Ilow ;and so 1024 ($0400) must be stored in two memory locations LDA #$04 STA Ihigh WhileLoop: LDA Ilow BNE NotZero LDA Ihigh BEQ EndLoop NotZero: JSR PrintI ;routine not implemented LSR Ihigh ;shift right ROR Ilow ;rotate right JMP WhileLoop

EndLoop: PLA ;restore accumulator from stack RTS ;return from subroutine</lang>

ActionScript

<lang actionscript>var i:int = 1024; while (i > 0) { 

   trace(i);
   i /= 2;

}</lang>

Ada

<lang ada>declare 

  I : Integer := 1024;

begin 

  while I > 0 loop
     Put_Line(Integer'Image(I));
     I := I / 2;
  end loop;

end;</lang>

ALGOL 68

Works with: ALGOL 68 version Revision 1 - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8-8d

<lang algol68>INT i := 1024; WHILE i > 0 DO 

  print(i);
  i := i OVER 2

OD</lang> Output: 

      +1024       +512       +256       +128        +64        +32        +16         +8         +4         +2         +1

AmigaE

<lang amigae>PROC main() 

 DEF i = 1024
 WHILE i > 0
   WriteF('\d\n', i)
   i := i / 2
 ENDWHILE

ENDPROC</lang>

AppleScript

AppleScript does not natively support a standard out. Use the Script Editor's Event Log as the output. <lang AppleScript >set i to 1024 repeat while i > 0 log i set i to i / 2 end repeat</lang>

AutoHotkey

<lang AutoHotkey>i = 1024 While (i > 0) { 

 output = %output%`n%i%
 i := Floor(i / 2)

} MsgBox % output</lang>

AWK

<lang awk>BEGIN { 

 v = 1024
 while(v > 0) {
   print v
   v = int(v/2)
 }

}</lang>

Bash

<lang bash>i=1024 while [ $i -gt 0 ]; do 

 echo $i
 ((i/=2))

done</lang>

BASIC

Works with: QuickBasic version 4.5

<lang qbasic>i = 1024 while i > 0 

  print i
  i = i / 2

wend</lang>

Befunge

<lang befunge>84*:*> :v 

    ^/2.:_@</lang>


C

<lang c>int i = 1024; while(i > 0) { 

 printf("%d\n", i);
 i /= 2;

}</lang> In for loop fashion: <lang c>int i; for(i = 1024;i > 0; i/=2){ 

  printf("%d\n", i);

}</lang>

C++

<lang cpp>int i = 1024; while(i > 0) { 

 std::cout << i << std::endl;
 i /= 2;

}</lang> Alternatively, it can be done with for: <lang cpp>for (int i = 1024; i>0; i /= 2) 

 std::cout << i << std::endl;</lang>

Indeed, in C++, <lang cpp>for (init; cond; update) 

 statement;</lang>

is equivalent to <lang cpp>{ 

 init;
 while (cond)
 {
   statement;
   update;
 }

}</lang>

C#

<lang csharp>int i = 1024; while(i > 0){ 

  System.Console.WriteLine(i);
  i /= 2;

}</lang>

Clojure

<lang lisp>(while (> @i 0) 

      (println @i)
      (dosync (ref-set i (quot @i 2))))</lang>

ColdFusion

Remove the leading space from the line break tag.

With tags: <lang cfm><cfset i = 1024 /> <cfloop condition="i GT 0"> 

 #i#< br />
 <cfset i /= 2 />

</cfloop></lang> With script: <lang cfm><cfscript> 

 i = 1024;
 while( i > 0 )
 {
   writeOutput( i + "< br/ >" );
 }

</cfscript></lang>

Common Lisp

<lang lisp>(setq i 1024) (loop while (> i 0) do 

 (print i)
 (setq i (floor i 2)))</lang>

D

<lang d>import std.stdio;

int i = 1024; void main() { 

   while(i > 0) {
       writefln("%s", i);
       i >>= 1;
   }

}</lang>

E

<lang e>var i := 1024 while (i > 0) { 

   println(i)
   i //= 2

}</lang>

Factor

<lang factor>1024 [ dup 0 > ] [ dup . 2 /i ] while drop</lang>

FALSE

<lang false>1024[$0>][$." "2/]#%</lang>

Forth

<lang forth>: halving ( n -- ) 

 begin  dup 0 >
 while  cr dup .  2/
 repeat drop ;

1024 halving</lang>

Fortran

Works with: Fortran version 90 and later

<lang fortran>INTEGER :: i = 1024 DO WHILE (i > 0) 

 WRITE(*,*) i
 i = i / 2

END DO</lang>

Go

<lang go>i := 1024 for i > 0 { 

 fmt.Printf("%d\n", i)
 i /= 2

}</lang>

Haskell

<lang haskell>import Control.Monad (when) main = loop 1024 

 where loop n = when (n > 0)
                     (do print n
                         loop (n `div` 2))</lang>

You could try to write a "while" that operates on monads:

<lang haskell>import Control.Monad (when)

whileM :: (Monad m) => m Bool -> m a -> m () whileM cond body = do c <- cond 

                     when c (body >> whileM cond body)</lang>

You can use it like this

<lang haskell>import Data.IORef

main :: IO () main = do r <- newIORef 1024 

         whileM (do n <- readIORef r
                    return (n > 0))
                (do n <- readIORef r
                    print n
                    modifyIORef r (`div` 2))</lang>

Icon and Unicon

Icon

<lang icon>procedure main() 

  local i
  i := 1024
  while write(0 < (i := i / 2))

end</lang>

Unicon

This Icon solution works in Unicon.

J

J is array-oriented, so there is very little need for loops. For example, one could satisfy this task this way:

<lang j>,. <.@-:^:*^:a: 1024</lang>

J does support loops for those times they can't be avoided (just like many languages support gotos for those time they can't be avoided).

<lang j>monad define 1024 

 while. 0 < y do.
   smoutput y
   y =. <. -: y 
 end.
 i.0 0

)</lang>

Note: this defines an anonymous function (monad define, and the subsequent lines) and passes it the argument 1024, which means it will be executed as soon as the full definition is available.

Java

<lang java5>int i = 1024; while(i > 0){ 

  System.out.println(i);
  i >>= 1; //also acceptable: i /= 2;

}</lang> With a for loop: <lang java5>for(int i = 1024; i > 0;i /= 2 /*or i>>= 1*/){ 

  System.out.println(i);

}</lang>

JavaScript

<lang javascript>var n = 1024; while (n>0) { 

print(n);
n/=2;

}</lang>

Joy

<lang joy>DEFINE putln == put '\n putch.

1024 [0 >] [dup putln 2 /] while.</lang>

Lisaac

<lang Lisaac>+ i : INTEGER; i := 1024; { i > 0 }.while_do { 

 i.print;
 '\n'.print;
 i := i / 2;

};</lang>

<lang logo>make "n 1024 while [:n > 0] [print :n make "n :n / 2]</lang>

Lua

<lang lua> n = 1024 while n>0 do 

 print(n)
 n = math.floor(n/2)

end </lang>

Mathematica

Mathematica does not support integer-rounding, it would result in getting fractions: 1/2, 1/4 , 1/8 and so on; the loop would take infinite time without using the Floor function: <lang Mathematica>i = 1024; While[i > 0, 

Print[i];
i = Floor[i/2];

]</lang>

MATLAB

In Matlab (like Octave) the math is done floating point, then rounding to integer, so that 1/2 will be always 1 and never 0. A 'floor' is used to round the number. <lang Matlab>i = 1024; while (i > 0) 

   disp(i);
   i = floor(i/2);

end</lang>

MAXScript

<lang maxscript>a = 1024 while a > 0 do ( 

   print a
   a /= 2

)</lang>

Make

<lang make>NEXT=`expr $* / 2` MAX=10

all: $(MAX)-n;

0-n:;

%-n: %-echo 

      @-make -f while.mk $(NEXT)-n MAX=$(MAX)

%-echo: 

      @echo $*</lang>

Invoking it <lang make>|make -f while.mk MAX=1024</lang>

Metafont

Metafont has no while loop, but it can be "simulated" easily.

<lang metafont>a := 1024; forever: exitif not (a > 0); 

 show a;
 a := a div 2;

endfor</lang>

MIRC Scripting Language

<lang mirc>alias while_loop { 

 var %n = 10
 while (%n >= 0) {
   echo -a Countdown: %n
   dec %n
 }

}</lang>

Modula-3

The usual module code and imports are omitted. <lang modula3>PROCEDURE DivBy2() = 

 VAR i: INTEGER := 1024;
 BEGIN
   WHILE i > 0 DO
     IO.PutInt(i);
     IO.Put("\n");
     i := i DIV 2;
   END;
 END DivBy2;</lang>

MOO

<lang moo>i = 1024; while (i > 0) 

 player:tell(i);
 i /= 2;

endwhile</lang>

Nimrod

<lang python>var n: int = 1024 while n > 0: 

 echo(n)
 n = n div 2</lang>

Oberon-2

The usual module code and imports are ommited. <lang oberon2>PROCEDURE DivBy2*(); 

 VAR i: INTEGER;

BEGIN 

 i := 1024;
 WHILE i > 0 DO
   Out.Int(i,0);
   Out.Ln;
   i := i DIV 2;
 END;

END DivBy2;</lang>

Objeck

<lang objeck> i := 1024; while(i > 0) { 

  i->PrintLine();
  i /= 2;

}; </lang>

OCaml

<lang ocaml>let n = ref 1024;; while !n > 0 do 

 Printf.printf "%d\n" !n;
 n := !n / 2

done;;</lang>

But it is more common to write it in a tail-recursive functional style: <lang ocaml>let rec loop n = 

 if n > 0 then begin
   Printf.printf "%d\n" n;
   loop (n / 2)
 end

in loop 1024</lang>

Octave

<lang octave>i = 1024; while (i > 0) 

 disp(i)
 i = floor(i/2);

endwhile</lang>

The usage of the type int32 is not convenient, since the math is done floating point, then rounding to integer, so that 1/2 will be always 1 and never 0.

Oz

Oz' for-loop can be used in a C-like manner: <lang oz>for I in 1024; I>0; I div 2 do 

  {Show I}

end</lang>

Alternatively, we can use the while feature of the for-loop with a mutable variable: <lang oz>declare 

 I = {NewCell 1024}

in 

 for while:@I > 0 do
    {Show @I}
    I := @I div 2
 end</lang>

Pascal

<lang pascal>program divby2(output);

var 

 i: integer;

begin 

 i := 1024;
 while i > 0 do
   begin
     writeln(i);
     i := i div 2
   end

end.</lang>

Perl

<lang perl>my $n = 1024; while ($n) { 

   print "$n\n";
   $n = int $n / 2;

}</lang>

until (condition) is equivalent to while (not condition).

<lang perl>my $n = 1024; until ($n <= 0) { 

   print "$n\n";
   $n = int $n / 2;

}</lang>

Perl 6

Note that +> is the Perl 6 right bit-shift operator, it is equivalent to dividing by two. The + indicates that it is a numeric operation, and the > indicates that it is the right bit-shift operation since the tag is pointing to the right.

<lang perl6>my $n = 1024*2;

say $n while ($n +>= 1) != 0;</lang>

Here is a solution without the restraints:

<lang perl6>say 1024 +> $_ for 0..10;</lang>

And here's how you'd really write it, using a series operator that intuits the division for you:

<lang perl6>for 1024, 512, 256 ... 1 { .say }</lang>

PHP

<lang php>$i = 1024; while ($i > 0) { 

  echo "$i\n";
  $i >>= 1;

}</lang>

PicoLisp

<lang PicoLisp>(let N 1024 

  (while (gt0 N)
     (println N)
     (setq N (/ N 2)) ) )</lang>

Pike

<lang pike>int main(){ 

  int i = 1024;
  while(i > 0){
     write(i + "\n");
     i = i / 2;
  }

}</lang>

PL/I

<lang PL/I> declare i fixed binary initial (1024);

do while (i>0); 

  put skip list (i);
  i = i / 2;

end; </lang>

Pop11

<lang pop11>lvars i = 1024; while i > 0 do 

   printf(i, '%p\n');
   i div 2 -> i;

endwhile;</lang>

PowerShell

<lang powershell>$i = 1024 while ($i -gt 0) { 

   $i
   $i /= 2

}</lang> Since PowerShell automatically converts variables to other types to accommodate for operations the above loop does not stop at 1 like it would in other languages but loops for quite a while until the value is small enough to be considered 0. An explicit cast corrects this: <lang powershell>$i = 1024 while ($i -gt 0) { 

   $i
   [int]$i /= 2

}</lang>

Prolog

<lang prolog>while(0) :- !. while(X) :- X>0,write(X), nl, X1 is X // 2, while(X1).</lang>

PureBasic

<lang PureBasic>If OpenConsole() 

 x.i = 1024
 While x > 0
   PrintN(Str(x))
   x / 2
 Wend

 Print(#CRLF$ + #CRLF$ + "Press ENTER to exit")
 Input()
 CloseConsole()

EndIf</lang>

Python

<lang python>n = 1024 while n > 0: 

   print n
   n //= 2</lang>

R

<lang R>i <- 1024L while(i > 0) { 

  print(i)
  i <- i %/% 2

}</lang>

REBOL

<lang REBOL>REBOL [ Title: "Loop/While" Author: oofoe Date: 2009-12-19 URL: http://rosettacode.org/wiki/Loop/While ]

value: 1024 while [value > 0][ print value value: to-integer value / 2 ]</lang>

REXX

Using integer division % here: <lang rexx>i = 1024 do while i > 0 

 say i
 i = i % 2

end</lang>

Ruby

<lang ruby>i = 1024 while i > 0 do 

  puts i
  i /= 2

end</lang> The above can be written in one statement (using the return value of the Kernel#puts method: nil is false), but the readability suffers: <lang ruby>i = 1024 puts i or i /= 2 while i > 0</lang>

until condition is equivalent to while not condition.

<lang ruby>i = 1024 until i <= 0 do 

  puts i
  i /= 2

end</lang>

Sather

<lang sather>class MAIN is 

 main is
   i ::= 1024;
   loop while!(i > 0);
     #OUT + i + "\n";
     i := i / 2;
   end;
 end;

end;</lang>

Scala

<lang scala>var i = 1024 while (i > 0) { 

 println(i)
 i /= 2

}</lang>

Scheme

<lang scheme>(do ((n 1024 (quotient n 2))) 

   ((<= n 0))
   (display n)
   (newline))</lang>

Seed7

<lang seed7>$ include "seed7_05.s7i";

const proc: main is func 

 local
   var integer: i is 1024;
 begin
   while i > 0 do
     writeln(i);
     i := i div 2
   end while;
 end func;</lang>

Slate

<lang slate>[| n | n: 1024. 

 [n isPositive] whileTrue: 
   [inform: number printString.
    n: n // 2]] do</lang>

Smalltalk

<lang smalltalk>number := 1024. [ number > 0 ] whileTrue: 

 [ Transcript print: number; nl.
 number := number // 2 ]</lang>

Standard ML

<lang sml>val n = ref 1024; while !n > 0 do ( 

 print (Int.toString (!n) ^ "\n");
 n := !n div 2

)</lang>

But it is more common to write it in a tail-recursive functional style: <lang sml>let 

 fun loop n =
   if n > 0 then (
     print (Int.toString n ^ "\n");
     loop (n div 2)
   ) else ()

in 

 loop 1024

end</lang>

Suneido

<lang Suneido>i = 1024 while (i > 0) 

   {
   Print(i)
   i = (i / 2).Floor()
   }</lang>

Output: <lang Suneido>1024 512 256 128 64 32 16 8 4 2 1</lang>

Tcl

<lang tcl>set i 1024 while {$i > 0} { 

   puts $i
   set i [expr {$i / 2}]

}</lang>

TI-89 BASIC

<lang ti89b>Local i 1024 → i While i > 0 

 Disp i
 intDiv(i, 2) → i

EndWhile</lang>

Trith

<lang trith>1024 [dup print 2 / floor] [dup 0 >] while drop</lang> <lang trith>1024 [dup print 1 shr] [dup 0 >] while drop</lang>

Unicon

See Icon.

UNIX Shell

Works with: Bourne Again SHell

<lang bash>x=1024 while $x -gt 0 ; do 

 echo $x
 x=$(( $x/2 ))

done</lang>

UnixPipes

<lang bash>(echo 1024>p.res;tail -f p.res) | while read a ; do 

  test $a -gt 0 && (expr $a / 2  >> p.res ; echo $a) || exit 0

done</lang>

Ursala

Unbounded iteration is expressed with the -> operator. An expression (p-> f) x, where p is a predicate and f is a function, evaluates to x, f(x), or f(f(x)), etc. as far as necessary to falsify p.

Printing an intermediate result on each iteration is a bigger problem because side effects are awkward. Instead, the function g in this example iteratively constructs a list of results, which is displayed on termination.

The argument to g is the unit list <1024>. The predicate p is ~&h, the function that tests whether the head of a list is non-null (equivalent to non-zero). The iterated function f is that which conses the truncated half of the head of its argument with a copy of the whole argument. The main program takes care of list reversal and formatting. <lang Ursala>#import nat

g = ~&h-> ^C/half@h ~&

  1. show+

main = %nP*=tx g <1024></lang> output: 

1024
512
256
128
64
32
16
8
4
2
1

Explicit iteration has its uses but there are always alternatives. The same output is produced by the following main program using bit manipulation. <lang Ursala>main = %nP*=tK33 1024</lang>

V

<lang v>1024 [0 >] [ 

  dup puts
  2 / >int

] while</lang>

Vedit macro language

<lang vedit>#1 = 1024 while (#1 > 0) { 

   Num_Type(#1)
   #1 /= 2

}</lang> or with for loop: <lang vedit>for (#1 = 1024; #1 > 0; #1 /= 2) { 

   Num_Type(#1)

}</lang>

Visual Basic .NET

<lang vbnet>Dim x = 1024 Do 

   Console.WriteLine(x)
   x = x \ 2

Loop While x > 0</lang>

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