Double Value2 = Convert.ToDouble(textBox1.Text);
Double Result = Value2;
if (Value2 == 0 && Oper == 4)
{
textBox1.Text = "На 0 делить нельзя!";
}
switch (Oper)
{
if(Oper == 1) {
}
else if(Oper == 2) {
}
switch (Oper)
{
case 1:
Result = Value + Value2;
break;
case 2:
Result = Value - Value2;
break;