c（#）如果textbox.text裏不是數字就給壹個提示框說輸入錯誤

private void button1_Click(object sender, EventArgs e)

{

double a, b;

try

{

a = Convert.ToDouble(textBox1.Text.ToString());

b = Convert.ToDouble(textBox2.Text.ToString());

}

catch

{

MessageBox.Show("輸入的不是數值！");

return;

}

string c = "+";

double d;

Form1 h = new Form1();

d = h.r(c, a, b);

label3.Text = Math.Round(d, 2).ToString();

}