/// <summary>
/// changes signs of the number
/// </summary>
private void PlusMinus()
{
// nothing to do for zero
if (DisplayNumber == "0")
{
return;
}
// convert negative number to positive
if (DisplayNumber[0] == '-')
{
DisplayNumber = DisplayNumber.Remove(0, 1);
}
// convert positive number to negative
else
{
DisplayNumber = "-" + DisplayNumber;
}
}
/// <summary>
/// add number character to number string (DisplayNumber)
/// </summary>
/// <param name="sender">the number or symbol entered by user</param>
/// <returns>DisplayNumber</returns>
protected void NumberAdd(string sender)
{
// start a new equation
if (endOfEquation)
{
endOfEquation = false;
}
// if previous entry was an operator, reset the number string
if (numberProcessing)
{
// change of signs is an exception
if (sender != "+/-")
{
DisplayNumber = "";
}
numberProcessing = false;
if (history[histIndex].GetOperSize() == 0)
{
Equation = "";
}
}
// change signs of the number
if (sender == "+/-")
{
PlusMinus();
}
// clear number string and equation
else if (sender == "C")
{
DisplayNumber = "0";
Equation = "";
history[histIndex].Clear();
}
// delete one character in number string
else if (sender == "B")
{
if (DisplayNumber.Length > 0)
{
DisplayNumber = DisplayNumber.Remove(DisplayNumber.Length - 1);
}
if (DisplayNumber == "")
{
DisplayNumber = "0";
}
}
// add the new number character to the number string
else
{
// if there is only "0" in the number string, remove it first
if (DisplayNumber == "0" && sender != ".")
{
DisplayNumber = "";
}
// if there is already a decimal point, do not add another
if (!(sender == "." && DisplayNumber.Contains('.')))
{
DisplayNumber += sender;
}
}
}