private void btnCompra_Click(object sender, EventArgs e)
    {
        this.Hide();
        Modal_compra compras = new Modal_compra();
        compras.ShowDialog();
        this.Close();


    }

public Modal_compra()
{
    InitializeComponent();

}

this.Close();

private void btnCompra_Click(object sender, EventArgs e)
{
    try
    {
        this.Hide();
        Modal_compra compras = new Modal_compra();
        compras.ShowDialog();
        //this.Close();
    }
    catch (Exception ex)
    {
         MessageBox.Show(ex.ToString());
    }
}