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
    if(!str) return 0;
    uint16_t result = 0, digit = 0;
    for(int i = 0; str[i] != '\0'; i++)
    {
        result <<= 4;
        if(str[i] >= '0' && str[i] <= '9')
        {
            digit = str[i] - '0';
        }
        else if(str[i] >= 'A' && str[i] <= 'F')
        {
            digit = str[i] - 'A' + 10;
        }
        else if(str[i] >= 'a' && str[i] <= 'f')
        {
            digit = str[i] - 'a' + 10;
        }
        result += digit;
    }
    return result;
}

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

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