#include <iostream>
#include <string>
#include <cmath>
#include <exception>
using namespace std;
 
int bintodec(string binary, unsigned int i = 0)
{
	int tot = 0;
	if (i < binary.length())
	{
		if (binary[i] == '1')
			tot = pow(2, i);
		else if (!binary[i] == '0')
			throw "String is not formatted in binary";
		return tot + bintodec(binary, ++i);
	}
	return tot;
}
 
int main() {
	string binary = "1011";
	int dec = bintodec(binary);
	cout << dec << endl;
	return 0;
}

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