运算表达式 栈应用

　　数据结构课作业栈应用之运算表达式求值。

#include <cstdio>
#include <iostream>
#include <cstring>
#include <string>
using namespace std;

#define Max 1005

template <typename T>
class Stack
{
    public:
        Stack ():myTop(-1) { memset (myArray, 0, sizeof myArray); }
        bool empty () const { return myTop == -1; }
        void push (T item);
        void pop ();
        T top () const;
    private:
        T myArray[Max];
        int myTop;
};
char tmp[25];

template <typename T> void Stack <T>::push (T item)
{
    if (myTop==Max) return;
    myArray[++myTop] = item;
}

template <typename T> void Stack <T>::pop ()
{
    if (myTop == -1) return;
    myTop--;
}

template <typename T> T Stack <T>::top () const
{
    if (myTop == -1) return -1;
    return myArray[myTop];
}

char OptrRelation[7][7] = 
{
      {'>', '>', '<', '<', '<', '>', '>'},  
      {'>', '>', '<', '<', '<', '>', '>'},  
      {'>', '>', '>', '>', '<', '>', '>'},  
      {'>', '>', '>', '>', '<', '>', '>'},  
      {'<', '<', '<', '<', '<', '=', ' '},  
      {'>', '>', '>', '>', ' ', '>', '>'},  
      {'<', '<', '<', '<', '<', ' ', '='}
};

int Postion_Optr (char optr)
{
    switch (optr)
    {
        case '+':return 0;
        case '-':return 1;
        case '*':return 2;
        case '/':return 3;
        case '(':return 4;
        case ')':return 5;
        case '#':return 6;
    }
}

char Precede (char s1, char s2)
{
    int coord_1 = Postion_Optr(s1);
    int coord_2 = Postion_Optr(s2);

    return OptrRelation[coord_1][coord_2];
}

int Opera (int a, char op, int b)
{
    if (op=='-') return a-b;
    if (op=='+') return a+b;
    if (op=='*') return a*b;
    if (op=='/') return a/b;
}

int Expression (string exp)
{
    Stack <char> Operator;
    Stack <int> Number;

    int i=0;
    exp += "#";
    Operator.push ('#');
    
    char ch = exp[i++];
    while (ch!='#' || Operator.top()!='#')
    {
        if (ch>='0' && ch<='9')
        {
            int k=0, a=0;
            while (ch<='9' && ch>='0')
            {
                tmp[k++] = ch;
                ch = exp[i++];
            }
            tmp[k] = '';
            sscanf (tmp, "%d", &a);
            Number.push (a);
        }
        else
        {
            switch (Precede (Operator.top(), ch))
            {
                case '<':
                    Operator.push (ch);
                           ch = exp[i++];
                    break;
                case '=':
                    Operator.pop ();
                           ch = exp[i++];
                    break;
                case '>':
                    char opt = Operator.top ();
                    Operator.pop();
                    int A = Number.top ();
                    Number.pop();
                    int B = Number.top ();
                    Number.pop();
                    Number.push (Opera (B, opt, A));
                    break;
            }
        }
    
    }
    return Number.top();
}

int main()
{
    string exp;
    while (1)
    {
        cout << "*** 请输入一个表达式 ***
"
            "注意：以'#'结尾且中间不得有多余的空格 ：
";cin >> exp;

        int ans = Expression (exp);

        printf ("%d
",ans);
    }
    return 0;
}