Help with a very simple C++ program?

I'm a 3rd semester programming student but I'm having a total blonde moment (plus c++ isn't my best language).. SO DON"T LAUGH!

All i need to do is a little mock-up for a future project.. I have the base of the mockup... display a title... let the user enter something, return a value (for display only, just a random number). Let the user continue to enter strings... but terminate the program when a blank string is entered (if the user hits enter).

Here is what i have, i just can't get it to exit on a blank line... is there a better way to do this? wtf am i missing, seriously, i have no idea why i can't get this stupid thing!

Help?

#include <iostream>

#include <string>

using namespace std;

int main() {

cout << "Expression Evaluator V1.0" << endl << endl;

string mockIn;

unsigned ct = 0;

do

{

mockIn = "";

cout << ">>";

cin >> mockIn;

cout << "[" << ct << "]" << " = 4321 " << endl;

ct++;

}while (mockIn != "");

return 0;

}