public ArrayList InputToPostfix()
{
Stack <Token> operatorStack = new Stack <Token>();
ArrayList postfixExpr = new ArrayList();
//loop over the tokenized infix expression from user input
try
{
foreach (Token currToken in inputTokens)
{
//if current token is an operand, add to output expression
if (currToken is Operand)
{
postfixExpr.Add(currToken);
}
else if (currToken is Operator)
{
//if current operator is a '(', add it to op stack
if (currToken.getValue().Equals("("))
{
operatorStack.Push(currToken);
}
//if current operator is a ')', pop from stack and add to output until '(' is encountered
else if (currToken.getValue().Equals(")"))
{
Token topStackToken = operatorStack.Pop();
while (!(topStackToken.getValue().Equals("(")))
{
postfixExpr.Add(topStackToken);
topStackToken = operatorStack.Pop();
}
}
//operators that are not parentheses
else
{
Operator currOpToken = currToken as Operator;
Operator currStackToken = new Operator("");
while ((!(operatorStack.Count() == 0)) && ((currStackToken = (Operator)operatorStack.Peek()).getPriority() >= currOpToken.getPriority()))
{
//add tokens from stack to output expression while the current token has <= priority than top of stack
currStackToken = operatorStack.Pop() as Operator;
postfixExpr.Add(currStackToken);
}
operatorStack.Push(currToken);
}
}
}
}
catch (System.InvalidOperationException)
{
return(new ArrayList());
}
//add remainder of stack to postfix expression
while (!(operatorStack.Count() == 0))
{
postfixExpr.Add(operatorStack.Pop());
}
return(postfixExpr);
}
