I wish

        int is_even(int n)
    {
        int result = -1;
        char number[8]; //should be enough
        sprintf(number, "%d", n);

        // check the number
        // TODO: handle negative numbers
        for (char *p=number; *p; p++)
        {
            if (*p=='0' || *p=='2' || *p=='4' || *p=='6' || *p=='8')
                result = 1;
            else if (*p=='1' || *p=='3' || *p=='5' || *p=='7' || *p=='9')
                result = 0;
            else {
               fprintf(stderr, "Your number is wrong!\n");
               exit(1); 
            }
        }
        return result;
    }