creating custom error page

Hi ..
I have two errors in my application i want to display a custom  defferent error page for each error...
Here is my code
protected void Button1_Click(object sender, EventArgs e)
    {
      
            int a = 10;
            int b = 0;
            int c = a / b;
     
      // FIRST ERROR
   

    }
    protected void Button2_Click(object sender, EventArgs e)
    {
       
       

            string str = "hjdfgjh";
& ...