Convert Hexadecimal String to Integer Without strtol or sscanf functions

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


int map(char c){
  

    if (c >= '0' && c <= '9')
        return c - '0';

    if (c >= 'A' && c <= 'F')
        return c - 'A' + 10;

    if (c >= 'a' && c <= 'f')
        return c - 'a' + 10;

    return 0; // invalid character

}
uint16_t hex_to_uint(const char *str) {
    // Your logic here
    int len=0;
    while(str[len]!='\0'){
        len++;
    }
    int result=0;
    int k;
    for(int i=0;i<len;i++){
        k=map(str[i]);
      result=result+(k)*(1<<4*(len-1-i));
    }
    return result;
}

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

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