static public Operand CreateOperand(string szVarName, Type varType)
{
return(OperandHelper.CreateOperand(szVarName, varType, null));
}
/// <summary>
/// Algo of GetPostFixNotation (source : Expression Evaluator : using RPN by lallous
/// in the C++/MFC section of www.CodeProject.com.
/// 1. Initialize an empty stack (string stack), prepare input infix expression and clear RPN string
/// 2. Repeat until we reach end of infix expression
/// I. Get token (operand or operator); skip white spaces
/// II. If token is:
/// a. Left parenthesis: Push it into stack
/// b. Right parenthesis: Keep popping from the stack and appending to
/// RPN string until we reach the left parenthesis.
/// If stack becomes empty and we didn't reach the left parenthesis
/// then break out with error "Unbalanced parenthesis"
/// c. Operator: If stack is empty or operator has a higher precedence than
/// the top of the stack then push operator into stack.
/// Else if operator has lower precedence then we keep popping and
/// appending to RPN string, this is repeated until operator in stack
/// has lower precedence than the current operator.
/// d. An operand: we simply append it to RPN string.
/// III. When the infix expression is finished, we start popping off the stack and
/// appending to RPN string till stack becomes empty.
///
/// </summary>
/// <param name=szExpr></param>
///
public ArrayList GetPostFixNotation(string szExpr, Type varType, bool bFormula)
{
Stack stkOp = new Stack();
ArrayList arrFinalExpr = new ArrayList();
string szResult = "";
Tokenizer tknzr = new Tokenizer(szExpr);
foreach (Token token in tknzr)
{
string szToken = token.Value.Trim();
if (szToken.Length == 0)
{
continue;
}
if (!OperatorHelper.IsOperator(szToken))
{
Operand oprnd = OperandHelper.CreateOperand(szToken, varType);
oprnd.ExtractAndSetValue(szToken, bFormula);
arrFinalExpr.Add(oprnd);
szResult += szToken;
continue;
}
string szOp = szToken;
if (szOp == "(")
{
stkOp.Push(szOp);
}
else if (szOp == ")")
{
string szTop;
while ((szTop = (string)stkOp.Pop()) != "(")
{
IOperator oprtr = OperatorHelper.CreateOperator(szTop);
arrFinalExpr.Add(oprtr);
szResult += szTop;
if (stkOp.Count == 0)
{
throw new RPN_Exception("Unmatched braces!");
}
}
}
else
{
if (stkOp.Count == 0 || (string)stkOp.Peek() == "(" ||
OperatorHelper.IsHigherPrecOperator(szOp, (string)stkOp.Peek()))
{
stkOp.Push(szOp);
}
else
{
while (stkOp.Count != 0)
{
if (OperatorHelper.IsLowerPrecOperator(szOp, (string)stkOp.Peek()) ||
OperatorHelper.IsEqualPrecOperator(szOp, (string)stkOp.Peek()))
{
string szTop = (string)stkOp.Peek();
if (szTop == "(")
{
break;
}
szTop = (string)stkOp.Pop();
IOperator oprtr = OperatorHelper.CreateOperator(szTop);
arrFinalExpr.Add(oprtr);
szResult += szTop;
}
else
{
break;
}
}
stkOp.Push(szOp);
}
}
}
while (stkOp.Count != 0)
{
string szTop = (string)stkOp.Pop();
if (szTop == "(")
{
throw new RPN_Exception("Unmatched braces");
}
IOperator oprtr = OperatorHelper.CreateOperator(szTop);
arrFinalExpr.Add(oprtr);
szResult += szTop;
}
return(arrFinalExpr);
}