Convert Hexadecimal String to Integer Without strtol or sscanf functions

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

uint16_t hex_to_uint(const char *str) {
    // Your logic here
    uint16_t res = 0x00;
    while(*str != '\0')
    {
        uint8_t digit;
        if(*str >= 'a' && *str <= 'z')
        {
           digit = 10 + (*str - 'a');
        }
        else if(*str >= '0' && *str <= '9')
        {
            digit = *str - '0';
        }
        else
        {
            digit = 10 + (*str - 'A');
        }
        res = (res*16) + digit;
        str++;
    }
    return res;
}

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

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