public double Evaluate()
{
Stack result = new Stack();
double oper1 = 0.0;
double oper2 = 0.0;
Token token = new Token();
foreach (object obj in output)
{
token = (Token)obj;
switch (token.Type)
{
case TokenType.Number:
result.Push(double.Parse(token.Value));
break;
case TokenType.Plus:
if (result.Count >= 2)
{
oper2 = (double)result.Pop();
oper1 = (double)result.Pop();
result.Push(oper1 + oper2);
}
else
{
throw new Exception("Evaluation error!");
}
break;
case TokenType.Minus:
if (result.Count >= 2)
{
oper2 = (double)result.Pop();
oper1 = (double)result.Pop();
result.Push(oper1 - oper2);
}
else
{
throw new Exception("Evaluation error!");
}
break;
case TokenType.Multiply:
if (result.Count >= 2)
{
oper2 = (double)result.Pop();
oper1 = (double)result.Pop();
result.Push(oper1 * oper2);
}
else
{
throw new Exception("Evaluation error!");
}
break;
case TokenType.Divide:
if (result.Count >= 2)
{
oper2 = (double)result.Pop();
oper1 = (double)result.Pop();
result.Push(oper1 / oper2);
}
else
{
throw new Exception("Evaluation error!");
}
break;
case TokenType.Exponent:
if (result.Count >= 2)
{
oper2 = (double)result.Pop();
oper1 = (double)result.Pop();
result.Push(Math.Pow(oper1, oper2));
}
else
{
throw new Exception("Evaluation error!");
}
break;
case TokenType.UnaryMinus:
if (result.Count >= 2)
{
oper1 = (double)result.Pop();
result.Push(-oper1);
}
else
{
throw new Exception("Evaluation error!");
}
break;
case TokenType.Ln:
if(result.Count >= 1)
{
oper1 = (double) result.Pop();
result.Push(Math.Log(oper1));
}
else
{
throw new Exception("Evaluation error!");
}
break;
case TokenType.Sqrt:
if(result.Count >= 1)
{
oper1 = (double) result.Pop();
result.Push(Math.Sqrt(oper1));
}
else
{
throw new Exception("Evaluation error!");
}
break;
case TokenType.Pow:
if(result.Count >= 1)
{
oper2 = (double) result.Pop();
oper1 = (double) result.Pop();
result.Push(Math.Pow(oper1, oper2));
}
else
{
throw new Exception("Evaluation error!");
}
break;
}
}
if (result.Count == 1)
{
return (double)result.Pop();
}
else
{
throw new Exception("Evaluation error");
}
}
public void Parse(string expression)
{
string buffer = expression.ToLower();
buffer = Regex.Replace(buffer, @"(?<number>\d+(\.\d+)?)", " ${number} ");
buffer = Regex.Replace(buffer, @"(?<ops>[+\-*/^()])", " ${ops} ");
buffer = Regex.Replace(buffer, @"\s+", " ").Trim();
buffer = Regex.Replace(buffer, "-", "MINUS");
buffer = Regex.Replace(buffer, @"(?<number>((\d+(\.\d+)?)))\s+MINUS", "${number} -");
buffer = buffer.Replace(") MINUS", ") -");
buffer = Regex.Replace(buffer, "(?<alpha>(ln|sqrt|pow))", " ${alpha} ");
buffer = Regex.Replace(buffer, "MINUS", "~"); //~ as unary '-' operator
buffer = Regex.Replace(buffer, ",", " ");
//tokenise
string[] parsed = buffer.Split(" ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
int i = 0;
double tokenValue;
Token token, opsToken = new Token();
for (i = 0; i < parsed.Length; ++i)
{
token = new Token();
token.Value = parsed[i];
token.Type = TokenType.None;
try
{
tokenValue = double.Parse(parsed[i]);
token.Type = TokenType.Number;
output.Enqueue(token);
}
catch (Exception)
{
switch (parsed[i])
{
case "+":
token.Type = TokenType.Plus;
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
while (IsOperatorToken(opsToken.Type))
{
output.Enqueue(ops.Pop());
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
}
else
{
break;
}
}
}
ops.Push(token);
break;
case "-":
token.Type = TokenType.Minus;
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
while (IsOperatorToken(opsToken.Type))
{
output.Enqueue(ops.Pop());
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
}
else
{
break;
}
}
}
ops.Push(token);
break;
case "*":
token.Type = TokenType.Multiply;
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
while (IsOperatorToken(opsToken.Type))
{
if (opsToken.Type == TokenType.Plus || opsToken.Type == TokenType.Minus)
{
break;
}
else
{
output.Enqueue(ops.Pop());
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
}
else
{
break;
}
}
}
}
ops.Push(token);
break;
case "/":
token.Type = TokenType.Divide;
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
while (IsOperatorToken(opsToken.Type))
{
if (opsToken.Type == TokenType.Plus || opsToken.Type == TokenType.Minus)
{
break;
}
else
{
output.Enqueue(ops.Pop());
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
}
else
{
break;
}
}
}
}
ops.Push(token);
break;
case "^":
token.Type = TokenType.Exponent;
ops.Push(token);
break;
case "~":
token.Type = TokenType.UnaryMinus;
ops.Push(token);
break;
case "(":
token.Type = TokenType.LeftParenthesis;
ops.Push(token);
break;
case ")":
token.Type = TokenType.RightParenthesis;
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
while (opsToken.Type != TokenType.LeftParenthesis)
{
output.Enqueue(ops.Pop());
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
}
else
{
throw new Exception("Wrong number of parenthesis");
}
}
ops.Pop();
}
if (ops.Count > 0)
{
opsToken = (Token)ops.Peek();
if (IsFunctionToken(opsToken.Type))
{
output.Enqueue(ops.Pop());
}
}
break;
case "ln":
token.Type = TokenType.Ln;
ops.Push(token);
break;
case "sqrt":
token.Type = TokenType.Sqrt;
ops.Push(token);
break;
case "pow":
token.Type = TokenType.Pow;
ops.Push(token);
break;
}
}
}
while (ops.Count != 0)
{
opsToken = (Token)ops.Pop();
if (opsToken.Type == TokenType.LeftParenthesis)
{
throw new Exception("Wrong number of parenthesis");
}
else
{
output.Enqueue(opsToken);
}
}
this.postfixExpression = string.Empty;
foreach (object obj in output)
{
opsToken = (Token)obj;
this.postfixExpression += string.Format("{0}", opsToken.Value);
}
}