/// <summary>
/// Takes an equation in infix format and parses it into postfix format. Each operator or number
/// is stored in a Command. The parsed, postfix format equation is then stored in a list of commands.
/// </summary>
/// <param name="infix">
/// The user's equation in infix format
/// </param>
/// <param name="factory">
/// The factory used to create commands
/// </param>
/// <returns>
/// Returns a list of commands for the user's equation in postfix format
/// </returns>
public List<Command> infixToPostfix(string infix, CommandFactory factory)
{
Command command;
List<Command> postfix = new List<Command>(); // Equation in postfix format
Stack<Command> tempStack = new Stack<Command>(); // Temporary stack of operators
int length = infix.Length;
for (int i = 0; i < length; i++)
{
char c = infix[i];
// Infix to Postfix algorithm
if (Char.IsNumber(c))
{
createNumber(c, factory, ref postfix, ref i, length, infix, false);
}
else if (c == '(')
{
command = factory.createLeftParenthesesCommand();
tempStack.Push(command);
}
else if (c == '^')
{
command = factory.createExponentCommand();
if ((tempStack.Count > 0) && (operatorCheck(Convert.ToChar(tempStack.Peek().getValue()), c, tempStack.Count)))
{
postfix.Add(tempStack.Pop());
}// end if
tempStack.Push(command);
}
else if (c == '*')
{
command = factory.createMultiplyCommand();
if ((tempStack.Count > 0) && (operatorCheck(Convert.ToChar(tempStack.Peek().getValue()), c, tempStack.Count)))
{
postfix.Add(tempStack.Pop());
}// end if
tempStack.Push(command);
}
else if (c == '/')
{
command = factory.createDivideCommand();
if ((tempStack.Count > 0) && (operatorCheck(Convert.ToChar(tempStack.Peek().getValue()), c, tempStack.Count)))
{
postfix.Add(tempStack.Pop());
}// end if
tempStack.Push(command);
}
else if (c == '%')
{
command = factory.createModulusCommand();
if ((tempStack.Count > 0) && (operatorCheck(Convert.ToChar(tempStack.Peek().getValue()), c, tempStack.Count)))
{
postfix.Add(tempStack.Pop());
}// end if
tempStack.Push(command);
}
else if (c == '+')
{
command = factory.createAddCommand();
if ((tempStack.Count > 0) && (operatorCheck(Convert.ToChar(tempStack.Peek().getValue()), c, tempStack.Count)))
{
postfix.Add(tempStack.Pop());
}// end if
tempStack.Push(command);
}
else if (c == '-')
{
string operators = "+-*/%";
if ((i != 0) && (operators.IndexOf(infix[i-1]) != -1) && (Char.IsNumber(infix[i + 1])))
{// if the index is not 0, index - 1 is an operator, and index + 1 is a number, then create a negative number
i++;
createNumber(infix[i], factory, ref postfix, ref i, length, infix, true);
}
else
{
// If infix[0] is '-', then append a 0 before appending the operator
if (i == 0)
{
command = factory.createNumberCommand(0);
postfix.Add(command);
}// end if
// If c == '-' and infix[i+1] == '-', then that is # - - #, which is # + #.
// Otherwise, it is a normal subtract command.
if (infix[i + 1] == '-')
{// # - - # = # + #
command = factory.createAddCommand();
i++;
}
else
{
command = factory.createSubtractCommand();
}// end if
if ((tempStack.Count > 0) && (operatorCheck(Convert.ToChar(tempStack.Peek().getValue()), c, tempStack.Count)))
{
postfix.Add(tempStack.Pop());
}// end if
tempStack.Push(command);
}
}
else if (c == ')')
{
command = factory.createRightParenthesesCommand();
while ((tempStack.Count > 0) && (Convert.ToChar(tempStack.Peek().getValue()) != '('))
{
postfix.Add(tempStack.Pop());
}// end while
// Pops off the left parentheses
if (tempStack.Count > 0)
{
tempStack.Pop();
}// end if
}
else
{
System.Diagnostics.Debug.WriteLine("Invalid Character: " + c);
}// end if
}// end foreach
// Adds the last operation to the postfix list.
while (tempStack.Count > 0)
{
postfix.Add(tempStack.Pop());
}// end while
return postfix;
}
private void createNumber(char c, CommandFactory factory, ref List<Command> postfix, ref int i, int length, string infix, bool isNegative)
{
Command command;
int numberLength = 0;
int currentIndex = i; // Copy current index
string strNumber = c.ToString(); // Convert the current character to a string
// Get index i+1 and check if it's an integer
while (currentIndex != (length - 1))
{
char c1 = infix[currentIndex + 1]; // Get the next character at index i+1
int intC1 = (int)char.GetNumericValue(c1); // Convert it to an integer
// Check if the next character is an integer.
if ((Char.IsNumber(c1)) && (intC1 >= 0) && (intC1 <= 9))
{
// Track number of digits in the number
numberLength++;
// Combines each character into strNumber if it's a number
strNumber += c1;
// Tracks the index number
currentIndex++;
}
else
{ // break out of the while loop if the character is not a number and update the index
break;
}// end if
}// end while
i += numberLength;
int number = 0;
// Catches an overflow exception if the number entered cannot fit in a 32bit integer.
try
{
number = checked(int.Parse(strNumber)); // Convert the string to an integer
}
catch (System.OverflowException e)
{
System.Web.HttpContext.Current.Response.Write(@"<script language='javascript'>alert('Error: Number Size\nThe number " + strNumber + "is too large or too small.');</script>");
System.Diagnostics.Debug.WriteLine(e.StackTrace);
}// end try
// Negates the number.
if (isNegative)
{
number *= -1;
}// end if
command = factory.createNumberCommand(number);
postfix.Add(command);
}