#include <stdio.h>

int my_isdigit(int c) { return (c >= '0' && c <= '9'); }
int my_isalpha(int c) { return ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')); }
int my_islower(int c) { return (c >= 'a' && c <= 'z'); }
int my_isupper(int c) { return (c >= 'A' && c <= 'Z'); }
int my_toupper(int c) { return my_islower(c) ? (c - 32) : c; }

int main(void) {
    char c = 'g';
    printf("Is '%c' a digit? %d\n", c, my_isdigit(c));
    printf("Is '%c' a letter? %d\n", c, my_isalpha(c));
    printf("Uppercase of '%c' is '%c'\n", c, my_toupper(c));
    return 0;
}