     private void button2_Click(object sender, EventArgs e)
        {
            textBox5.Visible = false;
            try
            {
                output = new FileStream("student.dat", FileMode.Append, FileAccess.Write);

            }
            catch (FileNotFoundException)
            {
                MessageBox.Show("File not exists");
                output.Close();
                return;
            }
            Record record = new Record();
            try
            {
                record.StNo = System.Convert.ToInt32(textBox1.Text);
                record.fName = textBox2.Text;
                record.lName = textBox3.Text;
                record.Grade = System.Convert.ToSingle(textBox4.Text);
            }
            catch (FormatException)
            {
                MessageBox.Show("Invalid Fromat");
                output.Close();
                return;
            }
            formatter.Serialize(output, record);
            output.Close();
            clearTextBox();


        }
