//simple function that turns a string into a Data node.
protected virtual ExpNode MakeDataNode(string operand)
{
double number;
bool isDouble = double.TryParse(operand, out number); //only stores the operand in number if it is actually a double
if (isDouble)
{
ValNode numNode = new ValNode(number); //makes a Numerical node with the operand's value
return(numNode);
}
else
{
VarNode varNode = new VarNode(operand); //makes a variable node with the operands variable name.
return(varNode);
}
}
public ExpTree(string expression)
{
Stack <string> equationStack = new Stack <string>();
Stack <string> treeStack = new Stack <string>();
Stack <Node> buildTree = new Stack <Node>();
string tempString = "";
//format expression to work with parser
expression = "(" + expression + ")";
char[] tokens = expression.ToCharArray();
//build stack from parsed expression - shunting yard algorithm
for (int i = 0; i < tokens.Length; i++)
{
if (tokens[i] == '(')
{
equationStack.Push(tokens[i].ToString());
}
else if (tokens[i] == ')') // doesn't push ")" to equation stack
{
while (equationStack.Peek() != "(") // pop until lhs bracket is found
{
treeStack.Push(equationStack.Pop()); // add right child and operator
}
equationStack.Pop(); // get rid of "("
}
else if (operators.Contains(tokens[i].ToString())) // current token is an operator
{
while (equationStack.Peek() != "(" &&
(!operators.Contains(equationStack.Peek()) ||
(getPrecedence(tokens[i].ToString()) < getPrecedence(equationStack.Peek())) || /*check if stack top is operator of higher precedence*/
(getPrecedence(tokens[i].ToString()) == getPrecedence(equationStack.Peek()))))
{
treeStack.Push(equationStack.Pop());
}
equationStack.Push(tokens[i].ToString());
}
else // integer or variable
{
// get numbers with multiple digits (will always execute at least once)
while (tokens[i] != '(' && tokens[i] != ')' && !operators.Contains(tokens[i].ToString()))
{
tempString += tokens[i];
i++;
}
if (tokens[i] == '(' || tokens[i] == ')' || operators.Contains(tokens[i].ToString()))
{
i--; //move back so token isn't skipped in next iteration
}
equationStack.Push(tempString);
tempString = "";
}
}
equationStack.Clear();
//reverse stack to get postfix expression
while (treeStack.Count != 0)
{
equationStack.Push(treeStack.Pop());
}
//build tree
while (equationStack.Count != 0) //equationStack now contains postfix expression
{
tempString = equationStack.Pop();
if (operators.Contains(tempString)) //make opNode
{
OpNode newNode = new OpNode(tempString);
if (buildTree.Count >= 2)
{
newNode.right = buildTree.Pop();
newNode.left = buildTree.Pop();
buildTree.Push(newNode);
}
}
else
{
if (tempString.All(Char.IsDigit)) //make valNode
{
ValNode newNode = new ValNode(tempString);
buildTree.Push(newNode);
}
else //make varNode
{
char let = Char.ToUpper(tempString[0]);
string row = tempString.Substring(1);
tempString = let + row;
if (!varDict.ContainsKey(tempString))
{
varDict[tempString] = 0; //initialize all variables to 0
}
VarNode newNode = new VarNode(tempString);
buildTree.Push(newNode);
varList.Add(tempString); //add to list of cell references
}
}
}
this.root = buildTree.Pop(); //final item in stack will be root node pointing to subtrees
}
