It converts hexadecimals to binary but it takes out some zeroes. I was told to use strings on the binary but not sure how to use them on binary to get it to output the zeroes it has been cutting off.

Hexdecimals to Binary

#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
	string hexaNumber,hexa,truebinaryNumber;
	int strlength,i,decimalNumber=0,hx,binary,iterator=0,binaryNumber=0;

	cout <<"Enter Hexa Number\n";
	cin >>hexaNumber;
	strlength = hexaNumber.length();
	
	for (i=0;i<strlength;i++)
	{
		hexa=hexaNumber.substr(i,1);
		if (hexa >="0" && hexa <= "9")
			cout <<"Your number is being converted "<<endl;
		else 
		{
			if (hexa =="a") 
				hexa = "10";
			else if (hexa =="b") 
				hexa="11";
			else if (hexa =="c")
				hexa ="12";
			else if (hexa =="d")
				hexa ="13";
			else if (hexa =="e")
				hexa ="14";
			else if (hexa =="f")
				hexa ="15";
			else if (hexa =="g")
				hexa ="16";
			else 
				cout <<"Invalid";
		}	//convert from string "hexa" to int "hex"
		hx = atoi (hexa.c_str());
		decimalNumber += hx * pow(16.0,strlength-i-1);
	}	

	while (decimalNumber>0)
	{
		binary = decimalNumber%2;
		binaryNumber += binary * pow(10.0,iterator);
		decimalNumber/=2;
		iterator++;
	}
	cout << binaryNumber<<endl;
 	system ("pause");

	return 0;
}