Help with a binary to decimal converter

[galaxie62]

Hello, I am doing a problem where I have to convert a random binary input via a string to a integer that is in decimal. I cant seem to figure out how to enter the equation into my function. Which is (((a[0]*2)+a[1])*2+a[2])*2+a[3]... . Currently I am trying to use a loop which goes through every 1 and 0 in the string and converts it into an integer. But after that I just cant think of how to get it to proceed any further along by plugging it into the function.I have tried doing a few things in the loop but none of them have worked so far. Can anyone help or give a hint as to how to let it convert every number in the string to an integer then allow me to input each one into a function?

#include <iostream>
#include <string>
using namespace std;

string a;

int input();

int main()
{
	input();

	int decimal, x, length, total = 0;
	length = a.length();
	
	for (x = 0; x < length; x++)
	{
		int num = a[x] - '0';
		num = num * 2;
		
	}
	
	cout << endl << total;
	a[1] * 2;
	cout << endl << a;

	int stop;
	cin >> stop;
	return 0;
}

int input()
{
	int x, x2, count, repeat = 0;
	
	while (repeat == 0)
	{
		cout << "Enter a string representing a binary number => ";
		cin >> a;
		count = a.length();
		for (x = 0; x < count; x++)
		{

			if (a[x] != '0' && a[x] != '1')
			{
				cout << a << "is not a string representing a binary number" << endl;
				repeat = 0;
				break;

			}
			else
				repeat = 1;
			
			

		}

	}
	return 0;
}

[coder777]

Change your for loop:

	for (x = 0; x < length; x++)
	{
		total = total * 2;
		total += a[x] - '0';
		
	}
	
	cout << endl << total;