isdigit
Header: <ctype.h>
Checks if the given character is a numeric character (0123456789).
# Declarations
int isdigit( int ch );
# Parameters
ch: character to classify
# Return value
Non-zero value if the character is a numeric character, zero otherwise.
# Notes
isdigit and isxdigit are the only standard narrow character classification functions that are not affected by the currently installed C locale, although some implementations (e.g. Microsoft in 1252 codepage) may classify additional single-byte characters as digits.
# Example
#include <ctype.h>
#include <limits.h>
#include <stdio.h>
int main(void)
{
for (int ndx = 0; ndx <= UCHAR_MAX; ++ndx)
if (isdigit(ndx))
printf("%c", ndx);
printf("\n");
}