C++ :: Using A Textbox And Other Items Between Multiple Forms

I am writing a program in Visual C++ 10 with 2 forms.

In the first form I have a textbox and a button. The button opens the second form.

In the second form, I have a button that changes the text in the textbox in form1 to an item from a listbox in form2.

Here is my problem. When I do the code for the button in form2 to change the textbox in form1 I get the errors:

error C2065: 'textBox1' : undeclared identifier
error C2227: left of '->Text' must point to class/struct/union/generic type

I thought maybe I should just include the "Form1.h" file but I can't do that because I already included "Form2.h" in form1 in order to be able to open the second form. If I try to include form1 in form2, it says that the code to open form2 is an error now.

My question is, how can I access identifiers such as "textbox1" from other forms and other files when I already used the first form to open the second form? I also want to know how to do this for all identifiers between all files.

how to print the selecteditem from a listbox into a textbox because that doesn't work by just setting them equal either.

Here is my code:

#pragma once
#include "Form2.h"
namespace Test1 {
using namespace System;

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