/// <summary>
/// process the postfix queue
/// http://btechsmartclass.com/DS/U2_T6.html
/// </summary>
/// <param name="queue">Postfix queue</param>
/// <returns>Result after processing queue</returns>
public static double ProcessPostfix(Queue <Token> queue)
{
Stack <Token> processingStack = new Stack <Token>();
while (queue.Count > 0)
{
Token token = queue.Peek();
TokenType tokenType = token.TokenType;
if (tokenType == TokenType.Numeric)
{
processingStack.Push(queue.Dequeue());
}
else if (tokenType == TokenType.Operator)
{
if (processingStack.Count < 2)
{
throw new ArgumentException("Invalid postfix: Stack too small");
}
// expect numeric tokens
NumericToken token1 = processingStack.Pop() as NumericToken;
NumericToken token2 = processingStack.Pop() as NumericToken;
if (token1 is null || token2 is null)
{
throw new ArgumentException("Invalid postfix: Trying to operate on tokens that are not operands");
}
OperatorToken operatorToken = queue.Dequeue() as OperatorToken;
double operationResult = Token.Operate(token2, token1, operatorToken);
processingStack.Push(TokenFactory.CreateToken(operationResult));
}
}
if (processingStack.Count != 1)
{
throw new ArgumentException("Invalid postfix: Stack doesn't have right count");
}
var numericToken = processingStack.Pop() as NumericToken;
if (numericToken is null)
{
throw new Exception("Something when wrong with the tokens!");
}
if (processingStack.Count > 0)
{
throw new Exception("Invalid postfix: Stack hasn't been emptied");
}
return(numericToken.NumericValue);;
}
/// <summary>
/// Operate on two tokens (operands)
/// </summary>
/// <param name="token1">first token</param>
/// <param name="token2">second token</param>
/// <param name="op">the operator</param>
/// <returns>output of operation</returns>
public static double Operate(NumericToken token1, NumericToken token2, OperatorToken op)
{
double value1 = token1.NumericValue;
double value2 = token2.NumericValue;
switch (op.Type)
{
case OperatorToken.OperatorType.Add:
return(value1 + value2);
case OperatorToken.OperatorType.Subtract:
return(value1 - value2);
case OperatorToken.OperatorType.Multiply:
return(value1 * value2);
case OperatorToken.OperatorType.Divide:
return(value1 / value2);
default:
throw new ArgumentException("Undefined operation");
}
}
