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;
    char ch;
    int i = 0;

    while ((ch = str[i++]) != '\0') {
        uint8_t val = 0;

        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;
        }  
        else {
            return 0xFFFF;
        }

        res = (res << 4) | val;  // nhân 16 + cộng giá trị mới
    }
    return res;
}

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

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

Solving Approach