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 result = 0;

    while (*str != '\0') {
        uint8_t tmp_oct; 
        if (*str >= '0' && *str <= '9') {
            tmp_oct = *str - '0';            
        } else if (*str >= 'A' && *str <= 'F') {
            tmp_oct = *str - 'A' + 10;
        } else if (*str >= 'a' && *str <= 'f') {
            tmp_oct = *str - 'a' + 10;
        } else {
            return 0;
        }

        result <<= 4;
        result |= tmp_oct;

        ++str;
    }

    return result;
}

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

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

Solving Approach