private void btnNajdiK_Click(object sender, EventArgs e)
 {
     try
     {
         k = kt.Select(Int32.Parse(tbIDK.Text));
         if (k == null)
         {
             MessageBox.Show("Klient s ID " + tbIDK.Text + " neexistuje", "Varovani", MessageBoxButtons.OK, MessageBoxIcon.Warning);
         }
         else
         {
             MessageBox.Show("Klient s ID " + tbIDK.Text + " existuje", "Informace", MessageBoxButtons.OK, MessageBoxIcon.Information);
         }
     }
     catch
     {
         MessageBox.Show("Zadejte spravne ID klienta", "Varovani", MessageBoxButtons.OK, MessageBoxIcon.Warning);
     }
 }