Problem in copying the text from the form to another

Well, ideally, you need to handle the textbox's Leave event so that you can wait for the user to finish typing before transferring the text to Form1:

        private void button2_Click(object sender, EventArgs e)

        {

            Form2 ff = new Form2();

            ff.textBox1.Leave += form2_textBox1_Leave;

            ff.Show();

        }

        // add this handler 'manually' not through the VS designer

        // to Form1

        private void form2_textBox1_Leave(object sender, EventArgs e)

        {

            TextBox tb = (TextBox)sender;

            if (tb.Text.Length > 0)

            {

                MessageBox.Show(tb.Text);

            }

        }

However, as Form2 stands, this won't work because the textbox is the only control on the form and so focus never leaves it.

You could handle the textbox's TextChanged event instead but, if you do this, then the MessageBox will pop up as each character is typed! So, if you're going to do this, then I'd add a label to Form1 and write to that:

        private void button2_Click(object sender, EventArgs e)

        {

            Form2 ff = new Form2();

            ff.textBox1.TextChanged += form2_textBox1_TextChanged;

            ff.Show();

        }

        // add this handler 'manually' not through the VS designer

        // to Form1

        private void form2_textBox1_TextChanged(object sender, EventArgs e)

        {

            TextBox tb = (TextBox)sender;

            label1.Text = tb.Text;

        }