//Convert binary to decimal.

#include <iostream>
#include <string>
#include<stdlib.h>                //for exit()
using namespace std;
int M(string x);
void error();

void main()
{
	string binNum;
	int decNum;

	cout<<"Please enter any binary number"<<endl;
	cin>>binNum;
	decNum=M(binNum);
	cout<<"The binary number "<<binNum<<" is equivalent to "
		<<decNum<<" in the decimal system."<<endl;
}

int M(string x)
{
	int n=x.size();
	if(n==0)
		return 0;
	else
		if(x[n-1]=='0')
		{
			x.resize(n-1);
			return 2*M(x);
		}
		else
			if(x[n-1]=='1')
			{
				x.resize(n-1);
				return 2*M(x)+1;
			}
			else
				error();
}

void error()
{
	cout<<"ha ha you messed up!!!"<<endl;
	exit(1);
}

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

int Mbin(string Bin);

void main()
{
   string num;
   int potatoe;

   cout<<"Enter binary number"<<endl;
   cin>>num;

   potatoe = Mbin(num);
   if(potatoe != -1)
     cout<<"the binary number of "<<num
     <<" is equal to "<<potatoe<<endl;
}

int Mbin(string Bin)
{
  int n=Bin.size();
  if(Bin=="1")
     return 1;
  else
     if(Bin == "0")
	return 0;
     else
	if(Bin[n-1]=='0')
	{
           Bin.resize(n-1);
	   return 2*Mbin(Bin);
	}
	else
	   if(Bin[n-1]=='1')
	   {
		Bin.resize(n-1);
		return 2*Mbin(Bin)+1;
	   }
	   else
	   {
	     cout<<"You did not enter a binary number"<<endl;
	     return -1;
	   }
}