How can I pass values from one form to another?

Question

Consider the situation where I have two windows forms, say F1 and F2. After using F1, I have now called F2.ShowDialog().

Answer 1

Use a defined Type for your information (class, struct...) and declare a variable of that in Form1

struct myData
{
    String str1;
    String str2;
}

Public Class Form1
{
  Public myData dat;
}

(Note: the type shouldnt really be public, this is just for the sake of this example) Thus the data sits within Form1. Modify the constructor of Form2 to accept a parameter of type Form1.

public Form2(Form1 frm1)
{
    mFrm1 = frm1;
    InitializeComponent();
}

Now, when you call form2, send in the very instance of Form1 that's making the call:

Form2 frm2 = new Form2(this);
frm2.ShowDialog();

Now, when execution has reached Form2, you can access the MyData within Form1:
mFrm1.dat;

In this way, both instances of Form1 and Form2 will be referencing the data that's in one place. Making changes/updates will be available for both instances of the forms.