Question

I have take 3 forms in visual studio 2008 with c# .net. In Form1 there are 2 buttons ,If i clicked on 1st button then Form2 will show & at same time i clicked on 2nd button then Form3 will show & already opened Form2 will hide.

Answer 1

//loop through all open forms
foreach (Form f in Application.OpenForms)
{
    if (f.Name != "Form1") //if it's not Form1
        f.Hide(); //then hide it (or close)
}
//show the form you want (ex: Form3)
new Form3().Show();