Exemple #1
0
        /**
         * 后缀表达式求值运算
         */
        public String getResult()
        {
            getBackExpression();
            String      operator1, operator2, tmp;
            int         index = 0;
            DefineStack ds    = new DefineStack();

            //String first = (String)ienumerator.Current;
            while (index < backExpression.Count)
            {
                tmp = (String)backExpression[index];
                //将栈顶两个操作数出栈,计算二者的值
                index++;
                if (CalculateUtil.isOperator(tmp))
                {
                    operator1 = (String)ds.pop();
                    operator2 = (String)ds.pop();
                    String tmpResult = CalculateUtil.twoOperate(tmp, operator1, operator2);
                    if (tmpResult.Equals("error"))
                    {
                        return("error");

                        break;
                    }
                    ds.push(tmpResult);
                }
                else
                {
                    ds.push(tmp);
                }
            }
            result = (String)ds.pop();
            return(result);
        }
Exemple #2
0
        /**
         * 转换中缀表达式为后缀表达式算法
         */
        private void getBackExpression()
        {
            DefineStack ds = new DefineStack();
            String      operators;
            int         position = 0;

            while (true)
            {
                if (CalculateUtil.isOperator((String)middleExpression[position]))
                {
                    //如果运算符为"(",直接存入运算符栈
                    if (ds.top == -1 || ((String)middleExpression[position]).Equals("("))
                    {
                        ds.push((String)middleExpression[position]);
                    }
                    //如果运算符是")",出操作符栈并添加到表达式顺序表中,直到遇到"("
                    else if (((String)middleExpression[position]).Equals(")"))
                    {
                        while (!((String)ds.getTop()).Equals("("))
                        {
                            operators = (String)ds.pop();
                            backExpression.Add(operators);
                        }
                        //这里需要弹出"("操作符
                        ds.pop();
                    }
                    //如果当前的运算符比栈顶的运算符优先级低,则输出栈顶运算符到顺序表,并将当前运算符压入运算符栈
                    else if (CalculateUtil.getPority((String)middleExpression[position]) <=
                             CalculateUtil.getPority((String)ds.getTop()) && (ds.top != -1))
                    {
                        operators = (String)ds.pop();
                        if (!operators.Equals("("))
                        {
                            backExpression.Add(operators);
                        }
                        ds.push((String)middleExpression[position]);
                    }
                    else
                    {
                        ds.push((String)middleExpression[position]);
                    }
                    position++;
                }
                //如果不是操作符,直接将操作数添加到顺序表中
                else
                {
                    backExpression.Add((String)middleExpression[position]);
                    position++;
                }
                if (position >= middleExpression.Count)
                {
                    break;
                }
            }
            while (ds.top != -1)
            {
                operators = (String)ds.pop();
                backExpression.Add(operators);
            }
        }