private void btnMdiAddCustomer_Click(object sender, EventArgs e)
 {
     if (Application.OpenForms["Add_New_Customer"] == null)
     {
         Add_New_Customer adcus = new Add_New_Customer();
         adcus.MdiParent = this;
         adcus.Size = new System.Drawing.Size(525, 620);
         adcus.Location = new System.Drawing.Point(150, 5);
         adcus.Show();
     }
 }
 private void ribCustomer_Click(object sender, EventArgs e)
 {
     Add_New_Customer addCustomer = new Add_New_Customer();
     addCustomer.MdiParent = this;
     addCustomer.Show();
 }