//very Important function-=-Self Explainatory
private void PopConnectPush()
{
ExpTreeNode Temp = OpStack.Pop(); //Get Top operator and associate the operands
//Find here if the Operator is "=" - then dont make the Symbol InVALID--Give some value
Temp._right = NodeStack.Pop(); //Get Left and right from NodeStck
if (Temp._value.ToString() == "=")
{
ExpTreeNode TmpLeft = NodeStack.Pop();
//Now this needs to be Symbol with no Sub tree
if (TmpLeft._ndType != ExpTreeNode.NodeType.Symbol)
{
ErrorException Er = new ErrorException("Operator = at the wrong Place Left Operand must be lvalue ");
throw Er;
}
if (TmpLeft._left == null || TmpLeft._right == null)
{
TmpLeft._value = -1; //SYMBOL TO BE CALCULATED
Temp._left = TmpLeft;
NodeStack.Push(Temp); // puch the sub tree on the stack
return;
}
else
{
ErrorException Er = new ErrorException("Operator = at the Wrong Place Left Operand must be lvalue");
throw Er;
}
}
Temp._left = NodeStack.Pop();
NodeStack.Push(Temp); // puch the sub tree on the stack
}
//Parse Expression funtion main funtion
//Creating the Exp tree from the Infix Expression
public ExpTreeNode ParseExpression(string exp)
{
//Check for the Expresiioon validity
if (!Isvalid_Exp(exp))
{
//Throw an Error Saying Commas are not proper
ErrorException Er = new ErrorException("Operators ( or ) are not at the right places");
throw Er;
//Is c# need this return after that -- i dont think so but anyway
}
//Fill ur _exp Variable will need that
_exp = exp;
NextToken();
do
{
//The errors that might come would be from stack
//If that went wrong -- gone case -- What use rwould do
//No USer specific Errors from this funtion
switch (current)
{
case Token.Literal:
//CreateLeafNode and push it on the stack
ExpTreeNode LNode = new ExpTreeNode();
LNode._value = literal;
LNode._ndType = ExpTreeNode.NodeType.Literal;
NodeStack.Push(LNode);
break;
case Token.Operator:
//pop the St
ExpTreeNode ONode = new ExpTreeNode();
ONode._value = Curr_op;
ONode._ndType = ExpTreeNode.NodeType.Operator;
if (Curr_op == "(")
{
OpStack.Push(ONode);
break;
}
if (Curr_op == ")")
{
while ("(" != (string)OpStack.Top._value)
{
PopConnectPush();
}
OpStack.Pop(); //Throw away {{
break;
}
if (OpStack.IsEmpty())
{
OpStack.Push(ONode);
}
else if ((string)OpStack.Top._value == "(")
{
OpStack.Push(ONode);
}
else if (Priority(OpStack.Top._value.ToString()) < Priority(ONode._value.ToString()))
{
OpStack.Push(ONode);
}
else
{
while (true)
{
PopConnectPush();
if (OpStack.IsEmpty() == true || (string)OpStack.Top._value == "(" || Priority(OpStack.Top._value.ToString()) < Priority(ONode._value.ToString()))
{
break;
}
}
OpStack.Push(ONode);
}
break;
case Token.Symbol:
{
ExpTreeNode SNode = new ExpTreeNode();
SNode._symbol = symbol;
SNode._ndType = ExpTreeNode.NodeType.Symbol;
NodeStack.Push(SNode);
}
break;
default:
break;
}
}while(NextToken() != Token.Eof);
while (OpStack.IsEmpty() == false)
{
PopConnectPush();
}
//Get the Top of the Node Stack thats the root
return(NodeStack.Top);
}