private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            cmbDay.Items.Clear();
            if (cmbMonth.Text.Trim() == "1" || cmbMonth.Text.Trim() == "3" || cmbMonth.Text.Trim() == "5" ||
                cmbMonth.Text.Trim() == "7" || cmbMonth.Text.Trim() == "8 " || cmbMonth.Text.Trim() == "10" ||
                cmbMonth.Text.Trim() == "12") 
            { 
                for (int a = 1; a  <= 31; a++) 
                { 
                    cmbDay.Items.Add(a); 
                } 
            }
            else if (cmbMonth.Text.Trim() == "4" || cmbMonth.Text.Trim() == "6" || cmbMonth.Text.Trim() == "8"
                || cmbMonth.Text.Trim() == "11") 
            { 
                for (int b = 1; b  <= 30; b++) 
                { 
                    cmbDay.Items.Add(b); 
                } 
            }  

        }