Convert Hexadecimal String to Integer Without strtol or sscanf functions

Code

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

uint16_t hex_to_uint(const char *str) {
    uint16_t res=0;
    for(int i=0;str[i];i++){
        int x=str[i]-'0';
        if(str[i]-'0'>=0 && str[i]-'0'<=9)
        res=res*16+str[i]-'0';
        else {
           
            for(int j=0;j<6;j++){
                if(tolower(str[i])-'a'==j){
                    res=res*16+(10+j);
                    break;
                }
                
            }
        }
    }
    return res;
}

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

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

Solving Approach