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) {
    int res = 0;
    int len = 0;
    int temp;
    while(*str){
        if(*str>='a' && *str<='f'){
            temp = (*str - 'a')+10;
        }else if(*str>='A' && *str<='F'){
            temp = (*str - 'A')+10;
        }else{
            temp = *str  - '0';
        }
        res = res*16 + temp;
        str++;
    }
    return res; 
}

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

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

Solving Approach