private void minusbtn_Click(object sender, EventArgs e)
{
minus = true;
plus = false;
mul = false;
div = false;
if (a == 0)
{
a = Convert.ToDouble(displaytxtbox.Text);
}
else
{
a = a - Convert.ToDouble(displaytxtbox.Text);
}
showtxtbox.Text = showtxtbox.Text + displaytxtbox.Text + "-";
displaytxtbox.Text = "";
when equal btn pressed,coding is...
if (minus)
{
b =a-Convert.ToDouble(displaytxtbox.Text);
displaytxtbox.Text = Convert.ToString(b);
a = 0;
}