public void PositiveNegativeButtonPress(string button)
{
if (LeftOperand != string.Empty && Operation == string.Empty)
{
_calculatorModel.ChangeLeftOperandSign();
Display = LeftOperand;
}
else if (RightOperand != string.Empty)
{
_calculatorModel.ChangeRightOperandSign();
Display = LeftOperand + Operation + RightOperand;
}
}
