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
    int res=0;
    int index=0;
    int val=0;
    while(str[index]!='\0'){
        char ch=str[index];
        res=res*16+val;
        if(ch>='0' && ch<='9'){
            val=ch-'0';
        }
        else if(ch>='A' && ch<='F'){
            val=ch-'A'+10;
        }
        else if(ch>='a' && ch<='f'){
            val=ch-'a'+10;
        }
        index++;
    }
    res=res*16+val;
    return res;
}

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

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

Solving Approach