Convert Binary String to Integer Without strtol function or Libraries

Code

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

uint16_t binary_to_uint(const char *str) {
    // Your logic here
    int len = 0;
    while (str[len] != '\0') ++len;

    // len = len - 1;
    // printf("%d", len);
    int res = 0;
    int i = 0;

    while (str[i] != '\0'){

        int tmp = (str[i] == '1') ? (1 << (len - 1)): (str[i] - '0')*(len - 1);
        res += tmp;
        ++i; --len;
    }
    return res;
}

int main() {
    char bin[20];
    scanf("%s", bin);

    printf("%u", binary_to_uint(bin));
    return 0;
}

Solving Approach