Previous Year Problem For Converting a Binary to Decimal Number

EDIT: This problem luckily came in the end sems too ;)

 So, I had seen this problem for doing the conversion as mentioned in the title, and I was thinking about the possible solutions. One of the approaches can be to use the number only which will be passed to a function but I thought of converting it to a string, and yes not to mention, you can pass an int to the function instead of a string, but you will need to convert it to a string and then work on that string as depicted, in the code pasted below.

Cvkkt Xjydib :)

#include <iostream>

#include<cstdlib>

#include<vector>

#include<math.h>

#include<string>

using namespace std;

/*

 *

 *    This program is contributed by Himesh Singh Chauhan

 *

 */

int bin_to_dec(string s){

    int itr=0;

    int ans=0;

    int s_size=s.size();

    int number=stoi(s);

    for(int i=s_size-1;i>=0;i--){

        int num;

        /*There was some cryptic error if I tried to convert a char 

         *to an int 

         */

        // char c=s[i];

        // num=atoi(c);

        int ascii_num=s[i];

        num=ascii_num-48;

        ans+=pow(2,itr) *num;

        itr++;

    }

    return ans;

}

int main(){

    cout<<"The answer receiverd from the 

bin_to_dec() is "<<bin_to_dec("11100111");

    return 0;

}