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) {
    // Your logic here
    uint16_t res = 0;

    for(uint8_t i=0;str[i]!='\0';i++){
        res <<= 4;
        if((str[i]>='a' && str[i]<='f')||(str[i]>='A' && str[i]<='F')){
            res |= (str[i]-'a'+10)&15;
        }else if(str[i]>='0' && str[i]<='9'){
            res |= (str[i]-'0')&15;
        }else{
            return 0;
        }
    }

    return res;
}

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

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

Solving Approach