public void compute_expression(string expr)
{
System.Collections.Generic.Stack<char> myStack = new System.Collections.Generic.Stack<char>();
string output = "";
// Rewriting the string into Reverse Polish Notation(RPN) format
foreach(char token in expr)
{
//Read a token.
//If the token is a number, then add it to the output queue.
if (Char.IsNumber(token) == true)
{
output = output + ' ' +token;
}
if(token == '+' || token == '-')
{
if (myStack.Count() != 0)
{
while(myStack.Peek() == '*' || myStack.Peek() == '/' || myStack.Peek() == '-')
{
if (myStack.Count() != 0)
{
output = output + ' ' + myStack.Peek();
myStack.Pop();
}
if (myStack.Count() == 0)
{
break;
}
}
}
myStack.Push(token);
}
if(token == '(')
{
myStack.Push(token);
}
if (token == ')')
{
if (myStack.Count() != 0)
{
while (myStack.Peek() != '(')
{
if (myStack.Count() != 0)
{
output = output + ' ' + myStack.Peek();
myStack.Pop();
}
}
myStack.Pop();
}
}
}
while(myStack.Count() != 0)
{
output = output + " " + myStack.Peek();
myStack.Pop();
}
//Done RPN
//Now we need to Evaluate the RPN
evalu(output);
}