/// <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);;
        }
示例#2
0
        /// <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");
            }
        }