Increment a value by 1 when button is clicked C++
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Have started a paper on C++ and have, what most experienced C++ programmers would call, a small problem...

I am using Visual Studio 2008 and coding in Visual C++ with .NET. I am trying to code the tiniest of applications that will add a new line into a textbox everytime a button is clicked. Adding new lines is simple enough, but I am wanting to add an incrementing integer with each line, e.g if I click on a button the first time, "This is line 1" gets added into the textbox, and on second click "This is line 2" gets added into the textbox. I am a little rusty on my programming and can't think of a looping structure that will enable this.

Here is the code (with some pseudocode) for the button's handler below:

    private: System::Void addLine_Click(System::Object^  sender, System::EventArgs^  e) {
    	
        int i = 0;
        if(button is clicked){
          listBox->Items->Add("This is line " + i);
          i++;
        }
    
    }

    Should output something like: 
    
    This is line 1
    This is line 2
    This is line 3
    This is line 4
    This is line 5
                 .
                 .
                 .
    This is line i

The name of my button is "addLine" and the name of the list box I want these lines to appear in is called "listBox".

Thanks in advance for helping this C++ noob :).