Determine if a string is numeric
Create a boolean function which takes in a string and tells whether it is a numeric string (floating point and negative numbers included).
You are encouraged to solve this task according to the task description, using any language you may know.
Ada
The first file is the package interface containing the declaration of the Is_Numeric function. <ada>
package Numeric_Tests is function Is_Numeric(Item : in String) return Boolean; end Numeric_Tests;
</ada> The second file is the package body containing the implementation of the Is_Numeric function. <ada>
package body Numeric_Tests is
----------------
-- Is_Numeric --
----------------
function Is_Numeric (Item : in String) return Boolean is
Result : Boolean := True;
begin
declare
Int : Integer;
begin
Int := Integer'Value(Item);
exception
when others =>
Result := False;
end;
if Result = False then
declare
Real : Float;
begin
Real := Float'Value(Item);
Result := True;
exception
when others =>
null;
end;
end if;
return Result;
end Is_Numeric;
end Numeric_Tests;
</Ada> The last file shows how the Is_Numeric function can be called. <Ada>
with Ada.Text_Io; use Ada.Text_Io; with Numeric_Tests; use Numeric_Tests; procedure Isnumeric_Test is S1 : String := "152"; S2 : String := "-3.1415926"; S3 : String := "Foo123"; begin Put_Line(S1 & " results in " & Boolean'Image(Is_Numeric(S1))); Put_Line(S2 & " results in " & Boolean'Image(Is_Numeric(S2))); Put_Line(S3 & " results in " & Boolean'Image(Is_Numeric(S3))); end Isnumeric_Test;
</Ada> The output of the program above is:
152 results in TRUE -3.1415926 results in TRUE Foo123 results in FALSE
ALGOL 68
PROC is numeric = (REF STRING string) BOOL: (
BOOL out := TRUE;
PROC call back false = (REF FILE f)BOOL: (out:= FALSE; TRUE);
FILE memory;
associate(memory, string);
on value error(memory, call back false);
on logical file end(memory, call back false);
UNION (INT, REAL, COMPLEX) numeric:=pi;
# use a FORMAT pattern instead of a regular expression #
getf(memory, ($gl$, numeric));
out
);
PROC is numeric test = VOID: (
STRING
s1 := "152",
s2 := "-3.1415926",
s3 := "Foo123";
print((s1, " results in ", is numeric(s1), new line));
print((s2, " results in ", is numeric(s2), new line));
print((s3, " results in ", is numeric(s3), new line))
);
is numeric test
Result is:
152 results in T -3.1415926 results in T Foo123 results in F
APL
⊃⎕VFI{w←⍵⋄((w='-')/w)←'¯'⋄w}'152 -3.1415926 Foo123'
1 1 0
C
Returns true (non-zero) if character-string parameter represents a signed or unsigned integer. Otherwise returns false (zero).
#include <stdlib.h>
int isNumeric (const char * s)
{
char * p;
strtol (s, &p, 10);
return !*p;
}
C#
Framework: .NET 2.0+
public static bool IsNumeric(string s)
{
double Result;
return double.TryParse(s, out Result); // TryParse routines were added in Framework version 2.0.
}
string value = "123";
if (IsNumeric(value))
{
// do something
}
Framework: .NET 1.0+
using System.Text.RegularExpressions;
public static bool IsNumeric(string s)
{
try
{
Double.Parse(s);
return true;
}
catch
{
return false;
}
}
ColdFusion
Adobe's ColdFusion
<cfset TestValue=34> TestValue: <cfoutput>#TestValue#</cfoutput>
<cfif isNumeric(TestValue)> is Numeric. <cfelse> is NOT Numeric. </cfif>
<cfset TestValue="NAS"> TestValue: <cfoutput>#TestValue#</cfoutput>
<cfif isNumeric(TestValue)> is Numeric. <cfelse> is NOT Numeric. </cfif>
D
<d> import std.stdio, std.string, std.conv, std.regexp;
bool isNumeric(string s) {
try
toDouble(s.strip());
catch (Error e)
return false;
return true;
}
bool isInt(string s) {
foreach (i, c; s) {
if (i == 0 && (c == '-' || c == '+'))
continue;
if (c >= '0' && c <= '9')
continue;
return
false;
}
return true;
}
bool isInt2(string s) {
return cast(bool)search(s, r"^[-+]?\d+$");
}
bool isInt3(string s) {
try
toInt(s.strip());
catch (Error e)
return false;
return true;
}
void main() {
foreach (s; ["12", " 12\t", "hello12", "-12", "0-12", "+12", "0x10", "6b"]) {
writefln("isNumeric(", s, ") = ", isNumeric(s));
writefln("isInt(", s, ") = ", isInt(s));
writefln("isInt2(", s, ") = ", isInt2(s));
writefln("isInt3(", s, ") = ", isInt3(s));
writefln();
}
} </d>
Forth
: is-numeric ( addr len -- )
2dup snumber? ?dup if \ not standard, but >number is more cumbersome to use
0< if
-rot type ." as integer = " .
else
2swap type ." as double = " <# #s #> type
then
else 2dup >float if
type ." as float = " f.
else
type ." isn't numeric in base " base @ dec.
then then ;
s" 1234" is-numeric \ 1234 as integer = 1234
s" 1234." is-numeric \ 1234. as double = 1234
s" 1234e" is-numeric \ 1234e as float = 1234.
s" $1234" is-numeric \ $1234 as integer = 4660 ( hex literal )
s" %1010" is-numeric \ %1010 as integer = 10 ( binary literal )
s" beef" is-numeric \ beef isn't numeric in base 10
hex
s" beef" is-numeric \ beef as integer = BEEF
s" &1234" is-numeric \ &1234 as integer = 4D2 ( decimal literal )
Haskell
This function is not particularly useful in a statically typed language. Instead, one would just attempt to convert the string to the desired type with read or reads, and handle parsing failure appropriately.
The task doesn't define which strings are considered "numeric", so we do Integers and Doubles, which should catch the most common cases (including hexadecimal 0x notation):
isInteger s = case reads s :: [(Integer, String)] of [(_, "")] -> True _ -> False isDouble s = case reads s :: [(Double, String)] of [(_, "")] -> True _ -> False isNumeric :: String -> Bool isNumeric s = isInteger s || isDouble s
One can easily add isRational, isComplex etc. following the same pattern.
IDL
function isnumeric,input on_ioerror, false test = double(input) return, 1 false: return, 0 end
Could be called like this:
if isnumeric('-123.45e-2') then print, 'yes' else print, 'no'
; ==> yes
if isnumeric('picklejuice') then print, 'yes' else print, 'no'
; ==> no
J
isNumeric=: _ ~: _".]
isNumericScalar=: [: (*./ *. 0=#@$) isNumeric
TXT=: ' is not a number.';' represents a scalar numeric value.'
sayIsNumericScalar=: , ;@(TXT{~isNumericScalar)
Examples of use:
isNumeric '152' 1 isNumeric '152 -3.1415926 Foo123' 1 1 0 isNumericScalar '152 -3.1415926 Foo123' 0 sayIsNumericScalar '-3.1415926' -3.1415926 represents a scalar numeric value.
Java
It's generally bad practice in Java to rely on an exception being thrown since exception handling is relatively expensive. If non-numeric strings are common, you're going to see a huge performance hit.
public boolean isNumeric(String input) {
try {
Integer.parseInt(input);
return true;
}
catch (NumberFormatException e) {
// s is not numeric
return false;
}
}
Alternative 1 : Check that each character in the string is number. Note that this will only works for integers.
private static final boolean isNumeric(final String s) {
for (int x = 0; x < s.length(); x++) {
final char c = s.charAt(x);
if (x == 0 && (c == '-')) continue; // negative
if ((c >= '0') && (c <= '9')) continue; // 0 - 9
return false; // invalid
}
return true; // valid
}
Alternative 2 : use a regular expression (a more elegant solution).
public static boolean isNumeric(String inputData) {
return inputData.matches("-?\\d+(.\\d+)?");
}
JavaScript
string value = "123.45e7";
if (isFinite(value))
{
// do something
}
//Or, in web browser in URL box:
// javascript:value="123.45e4"; if(isFinite(value)) {alert('numeric')} else {alert('non-numeric')}
Logo
show number? "-1.23 ; true
MAXScript
fn isNumeric str =
(
try
(
(str as integer) != undefined
)
catch(false)
)
isNumeric "123"
mIRC Scripting Language
var %value = 3
if ($1 isnum) {
echo -s $1 is numeric.
}
Objective-C
The NSScanner class supports scanning of strings for various types. The scanFloat method will return TRUE if the string is numeric, even if the number is actually too long to be contained by the precision of a float.
if( [[NSScanner scannerWithString:@"-123.4e5"] scanFloat:nil] ) NSLog( @"\"-123.4e5\" is numeric" ); else NSLog( @"\"-123.4e5\" is not numeric" ); if( [[NSScanner scannerWithString:@"Not a number"] scanFloat:nil] ) NSLog( @"\"Not a number\" is numeric" ); else NSLog( @"\"Not a number\" is not numeric" ); // prints: "-123.4e5" is numeric // prints: "Not a number" is not numeric
OCaml
This function is not particularly useful in a statically typed language. Instead, one would just attempt to convert the string to the desired type and handle parsing failure appropriately.
The task doesn't define which strings are considered "numeric", so we do ints and floats, which should catch the most common cases:
let is_int s = try ignore (int_of_string s); true with _ -> false let is_float s = try ignore (float_of_string s); true with _ -> false let is_numeric s = is_int s || is_float s
Perl
Quoting from perlfaq4:
How do I determine whether a scalar is a number/whole/integer/float?
Assuming that you don't care about IEEE notations like "NaN" or "Infinity", you probably just want to use a regular expression.
if (/\D/) { print "has nondigits\n" }
if (/^\d+$/) { print "is a whole number\n" }
if (/^-?\d+$/) { print "is an integer\n" }
if (/^[+-]?\d+$/) { print "is a +/- integer\n" }
if (/^-?\d+\.?\d*$/) { print "is a real number\n" }
if (/^-?(?:\d+(?:\.\d*)?&\.\d+)$/) { print "is a decimal number\n" }
if (/^([+-]?)(?=\d&\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/)
{ print "a C float\n" }
There are also some commonly used modules for the task. Scalar::Util (distributed with 5.8) provides access to Perl's internal function "looks_like_number" for determining whether a variable looks like a number. Data::Types exports functions that validate data types using both the above and other regular expressions. Thirdly, there is "Regexp::Common" which has regular expressions to match various types of numbers. Those three modules are available from the CPAN.
If you're on a POSIX system, Perl supports the "POSIX::strtod" function. Its semantics are somewhat cumbersome, so here's a "getnum" wrapper function for more convenient access. This function takes a string and returns the number it found, or "undef" for input that isn't a C float. The "is_numeric" function is a front end to "getnum" if you just want to say, Is this a float?
sub getnum {
use POSIX qw(strtod);
my $str = shift;
$str =~ s/^\s+//;
$str =~ s/\s+$//;
$! = 0;
my($num, $unparsed) = strtod($str);
if (($str eq ) && ($unparsed != 0) && $!) {
return undef;
} else {
return $num;
}
}
sub is_numeric { defined getnum($_[0]) }
Or you could check out the String::Scanf module on the CPAN instead. The POSIX module (part of the standard Perl distribution) provides the "strtod" and "strtol" for converting strings to double and longs, respectively.
PHP
<?php
$string = '123';
if(is_numeric($string)) {
}
PL/SQL
FUNCTION IsNumeric( value IN VARCHAR2 )
RETURN BOOLEAN
IS
help NUMBER;
BEGIN
help := to_number( value );
return( TRUE );
EXCEPTION
WHEN others THEN
return( FALSE );
END;
Value VARCHAR2( 10 ) := '123';
IF( IsNumeric( Value ) )
THEN
NULL;
END IF;
Python
<python>s = '123' try:
i = float(s)
except ValueError:
# not numeric
else:
# numeric</python>
Or for positive integers only:
<python>s = '123' if s.isdigit():
# numeric</python>
Including complex, hex, binary, and octal numeric literals we get: <python>def is_numeric(lit):
'Return value of numeric literal string or ValueError exception'
# Hex/Binary
litneg = lit[1:] if lit[0] == '-' else lit
if litneg[0] == '0':
if litneg[1] in 'xX':
return int(lit,16)
elif litneg[1] in 'bB':
return int(lit,2)
else:
try:
return int(lit,8)
except ValueError:
pass
# Int/Float/Complex
try:
return int(lit)
except ValueError:
pass
try:
return float(lit)
except ValueError:
pass
return complex(lit)
</python> Sample use: <python>>>> for s in ['123', '-123.', '-123e-4', '0123', '0x1a1', '-123+4.5j', '0b0101', '0.123', '-0xabc', '-0b101']:
print "%14s -> %-14s %s" % ('"'+s+'"', is_numeric(s), type(is_numeric(s)))
"123" -> 123 <type 'int'>
"-123." -> -123.0 <type 'float'>
"-123e-4" -> -0.0123 <type 'float'>
"0123" -> 83 <type 'int'>
"0x1a1" -> 417 <type 'int'>
"-123+4.5j" -> (-123+4.5j) <type 'complex'>
"0b0101" -> 5 <type 'int'>
"0.123" -> 0.123 <type 'float'>
"-0xabc" -> -2748 <type 'int'>
"-0b101" -> -5 <type 'int'>
>>> </python>
Ruby
value=123
if Numeric===value
...
Scheme
number? is a standard R5RS scheme predicate
(define is-numeric? number?)
SQL
declare @s varchar(10) set @s = '1234.56' print isnumeric(@s) --prints 1 if numeric, 0 if not. if isnumeric(@s)=1 begin print 'Numeric' end else print 'Non-numeric'
Tcl
if { [string is double $varname] } then { ... }
Also string is integer (, string is alnum etc etc)
Toka
Returns a flag of TRUE if character-string parameter represents a signed or unsigned integer. Otherwise returns a flag of FALSE. The success or failure is dependent on the source is valid in the current numeric base. The >number function also recognizes several optional prefixes for overriding the current base during conversion.
[ ( string -- flag )
>number nip ] is isNumeric
( Some tests )
decimal
" 100" isNumeric . ( succeeds, 100 is a valid decimal integer )
" 100.21" isNumeric . ( fails, 100.21 is not an integer)
" a" isNumeric . ( fails, 'a' is not a valid integer in the decimal base )
" $a" isNumeric . ( succeeds, because $ is a valid override prefix )
( denoting that the following character is a hexadecimal number )
VBScript
IsNumeric(Expr)
Returns a True if numeric and a false if not.
Visual Basic .NET
Dim Value As String = "+123
"
If IsNumeric(Value) Then
End If