isdigit -- Test for Numeric Character


SYNOPSIS
#include <ctype.h>
int isdigit(int c);
DESCRIPTION
isdigit
tests an integer value to determine whether it is a numeric
character (digit).
RETURN VALUE
isdigit
returns 0 if the character is not a digit, or a nonzero
value if it is. If the argument is EOF
, 0 is returned.
CAUTION
The effect of isdigit
on a noncharacter argument other than EOF
is undefined. Do not assume that isdigit
returns either 0 or 1.
EXAMPLE
#include <ctype.h>
#include <stdio.h>
#define IDMAX 40
main()
{
char id[IDMAX+1];
char *text;
char input[IDMAX];
int i;
puts("Enter a string of numbers/characters (maximum 40):");
text = gets(input);
/* Copy a string of digits from text to id. */
for (i = 0; i < IDMAX && isdigit(text[i]); ++i)
id[i] = text[i];
id[i] = '0';
/* Only the digits should be copied. */
printf("You first entered these digits: %sn", id);
}
RELATED FUNCTIONS
isxdigit
SEE ALSO
Character Type Macros and Functions