private void btnEqual_Click(object sender, EventArgs e)
{
second = double.Parse(tbxScreen.Text);
double Su;
double Mi;
double Mu;
double Di;
switch (operation)
{
case "+":
Su = obj.Sum((first), (second));
tbxScreen.Text = Su.ToString();
break;
case "-":
Mi = obj2.Minus((first), (second));
tbxScreen.Text = Mi.ToString();
break;
case "*":
Mu = obj3.Multiply((first), (second));
tbxScreen.Text = Mu.ToString();
break;
case "/":
Di = obj4.Divide((first), (second));
tbxScreen.Text = Di.ToString();
break;
}
}