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

/*
Loop right to left through the characters of the string
with a "reverse iterator" it.
Use the funcions begin and end for a plain old iterator,
Use the funcions rbegin and rend for a reverse iterator.
*/

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

	for (auto it {rbegin(s)}; it != rend(s); ++it) {
		if (*it == '1') {   // *it is each character of the string
			sum += power;
		} else if (*it != '0') {
			cerr << "Bad character '" << *it << "' in string.\n";
			return EXIT_FAILURE;
		}

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

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