Reference
C Library
IOstream Library
Strings library
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Miscellaneous
C Library
cassert (assert.h)
cctype (ctype.h)
cerrno (errno.h)
cfloat (float.h)
ciso646 (iso646.h)
climits (limits.h)
clocale (locale.h)
cmath (math.h)
csetjmp (setjmp.h)
csignal (signal.h)
cstdarg (stdarg.h)
cstddef (stddef.h)
cstdio (stdio.h)
cstdlib (stdlib.h)
cstring (string.h)
ctime (time.h)
cctype (ctype.h)
isalnum
isalpha
iscntrl
isdigit
isgraph
islower
isprint
ispunct
isspace
isupper
isxdigit
tolower
toupper


isdigit

function
<cctype> 
int isdigit ( int c );

Check if character is decimal digit

Checks if parameter c is a decimal digit character.

Decimal digits are any of: 0 1 2 3 4 5 6 7 8 9
For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header.

In C++, a locale-specific template version of this function (isdigit) exists in header <locale>.

Parameters

c
Character to be checked, casted to an int, or EOF.

Return Value

A value different from zero (i.e., true) if indeed c is a decimal digit. Zero (i.e., false) otherwise.

Example

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/* isdigit example */
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int main ()
{
  char str[]="1776ad";
  int year;
  if (isdigit(str[0]))
  {
    year = atoi (str);
    printf ("The year that followed %d was %d.\n",year,year+1);
  }
  return 0;
}


isdigit is used to check if the first character in str is a digit and therefore a valid candidate to be converted by atoi into an integer value.

See also

isalnum Check if character is alphanumeric (function)
isalpha Check if character is alphabetic (function)