Increment a value by 1 when button is clicked C++

Question

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, eg 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 :).

Answer 1

i is a local variable so it will loose its scope whenever the function exits. Either you need to declare i as static or make it as a class variable.

private: System::Void addLine_Click(System::Object^  sender, System::EventArgs^  e) {

    static int i = 0;
    if(button is clicked){
      listBox->Items->Add("This is line " + i);
      i++;
    }

}

Answer 2

我需要成为该类的成员-否则增量将无法在函数调用中幸免。