#include <iostream>
#include <cstdlib>
#include <string>  //for class string
using namespace std;

/*
Loop from right to left through the characters of the string.
The string contains s.size() characters.
The rightmost character is at subscript s.size() - 1.
The leftmost character is at subscript 0.
*/

int main()
{
	cout << "Please input an integer in binary: ";
	string s;
	cin >> s;

	if (!cin) {
		cerr << "Sorry, I couldn't receive that.\n";
		return EXIT_FAILURE;
	}

	int power {1}; //Runs through the powers of 2: 1, 2, 4, 8, 16, 32, etc.
	int sum {0};

	for (int i = s.size() - 1; i >= 0; --i) {
		if (s[i] == '1') {   //s[i] is each character of the string s
			sum += power;
		} else if (s[i] != '0') {
			cerr << "Bad character '" << s[i] << "' in string.\n";
			return EXIT_FAILURE;
		}

		power *= 2;   //means power = power * 2;
	}

	cout << "binary " << s << " = decimal " << sum << "\n";
	return EXIT_SUCCESS;
}