Convert Hexadecimal String to Integer Without strtol or sscanf functions

Code

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

uint16_t hex_to_uint(const char *str) {
    uint16_t res = 0, idx = 0;

    while(str[idx] != '\0') {
        res <<=  4;
        if (str[idx] >= 'A' && str[idx] <= 'F') {
            res |= (str[idx] - 'A' + 10);
        } else if (str[idx] >= 'a' && str[idx] <= 'f') {
            res |= (str[idx] - 'a' + 10);
        } else {
            res |= (str[idx] - '0');
        }
        
        idx++;
    }


    return res;
}

int main() {
    char hex[10];
    scanf("%s", hex);

    printf("%u", hex_to_uint(hex));
    return 0;
}

Solving Approach