C++利用权重方法将二进制正数转换为十进制数

#include <iostream>
#include <Windows.h>
#include <string>

using namespace std;

int main(void) {
    string str;
    int p = ; //记录当前二进制权重
    int s = ;

    cout << "请输入一个二进制数：";
    cin >> str;

    for (int i = str.length()-; i >= ; i--) {
        int x = str[i] - ''; // '0' - '0' = 0  '1' - '0' = 1
        s += x * p;
        p *= ; // p = p * 2
    }
    cout << s << endl;
    system("pause");
    return ;
}