private void button2_Click(object sender, EventArgs e)
 {
     Form4 form4 = new Form4();
     form4.Show();
     this.Hide();
 }
        private void celToFahToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form4 CelToFah = new Form4();

            CelToFah.Show();
        }