isnum() in c code example

Example 1: isdigit in c

#include <stdio.h>
#include <ctype.h>

int main()
{
    char c;
    c='0';
    printf("Result when numeric character is passed: %d", isdigit(c));

    c='+';
    printf("\nResult when non-numeric character is passed: %d", isdigit(c));

    return 0;
}

Example 2: c check if char is number

char c = 'a'; // or whatever

if (isalpha(c)) {
    puts("it's a letter");
} else if (isdigit(c)) {
    puts("it's a digit");
} else {
    puts("something else?");
}