Convert Integer to Hex String Without sprintf or itoa functions

Code

#include <stdio.h>
#include <stdint.h>

void print_hex(uint16_t num) {
    char char_map[] = "0123456789ABCDEF";
    char str[4];
    int idx = 0;

    while (num >= 0) {
        str[idx++] = char_map[num & 0xF];
        num >>= 4;
        if (num == 0)
            break;
    }

    for (int i = idx - 1; i >= 0; i--) {
        putchar(str[i]);
    }
}

int main() {
    uint16_t num;
    scanf("%hu", &num);
    print_hex(num);
    return 0;
}

Solving Approach