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。

  1 #include <cstdio>
  2 #include <iostream>
  3 #include <cstring>
  4 #include <string>
  5 using namespace std;
  6 
  7 #define Max 1005
  8 
  9 template <typename T>
 10 class Stack
 11 {
 12     public:
 13         Stack ():myTop(-1) { memset (myArray, 0, sizeof myArray); }
 14         bool empty () const { return myTop == -1; }
 15         void push (T item);
 16         void pop ();
 17         T top () const;
 18     private:
 19         T myArray[Max];
 20         int myTop;
 21 };
 22 char tmp[25];
 23 
 24 template <typename T> void Stack <T>::push (T item)
 25 {
 26     if (myTop==Max) return;
 27     myArray[++myTop] = item;
 28 }
 29 
 30 template <typename T> void Stack <T>::pop ()
 31 {
 32     if (myTop == -1) return;
 33     myTop--;
 34 }
 35 
 36 template <typename T> T Stack <T>::top () const
 37 {
 38     if (myTop == -1) return -1;
 39     return myArray[myTop];
 40 }
 41 
 42 char OptrRelation[7][7] = 
 43 {
 44       {'>', '>', '<', '<', '<', '>', '>'},  
 45       {'>', '>', '<', '<', '<', '>', '>'},  
 46       {'>', '>', '>', '>', '<', '>', '>'},  
 47       {'>', '>', '>', '>', '<', '>', '>'},  
 48       {'<', '<', '<', '<', '<', '=', ' '},  
 49       {'>', '>', '>', '>', ' ', '>', '>'},  
 50       {'<', '<', '<', '<', '<', ' ', '='}
 51 };
 52 
 53 int Postion_Optr (char optr)
 54 {
 55     switch (optr)
 56     {
 57         case '+':return 0;
 58         case '-':return 1;
 59         case '*':return 2;
 60         case '/':return 3;
 61         case '(':return 4;
 62         case ')':return 5;
 63         case '#':return 6;
 64     }
 65 }
 66 
 67 char Precede (char s1, char s2)
 68 {
 69     int coord_1 = Postion_Optr(s1);
 70     int coord_2 = Postion_Optr(s2);
 71 
 72     return OptrRelation[coord_1][coord_2];
 73 }
 74 
 75 int Opera (int a, char op, int b)
 76 {
 77     if (op=='-') return a-b;
 78     if (op=='+') return a+b;
 79     if (op=='*') return a*b;
 80     if (op=='/') return a/b;
 81 }
 82 
 83 int Expression (string exp)
 84 {
 85     Stack <char> Operator;
 86     Stack <int> Number;
 87 
 88     int i=0;
 89     exp += "#";
 90     Operator.push ('#');
 91     
 92     char ch = exp[i++];
 93     while (ch!='#' || Operator.top()!='#')
 94     {
 95         if (ch>='0' && ch<='9')
 96         {
 97             int k=0, a=0;
 98             while (ch<='9' && ch>='0')
 99             {
100                 tmp[k++] = ch;
101                 ch = exp[i++];
102             }
103             tmp[k] = '\0';
104             sscanf (tmp, "%d", &a);
105             Number.push (a);
106         }
107         else
108         {
109             switch (Precede (Operator.top(), ch))
110             {
111                 case '<':
112                     Operator.push (ch);
113                            ch = exp[i++];
114                     break;
115                 case '=':
116                     Operator.pop ();
117                            ch = exp[i++];
118                     break;
119                 case '>':
120                     char opt = Operator.top ();
121                     Operator.pop();
122                     int A = Number.top ();
123                     Number.pop();
124                     int B = Number.top ();
125                     Number.pop();
126                     Number.push (Opera (B, opt, A));
127                     break;
128             }
129         }
130     
131     }
132     return Number.top();
133 }
134 
135 int main()
136 {
137     string exp;
138     while (1)
139     {
140         cout << "*** 请输入一个表达式 ***\n"
141             "注意：以'#'结尾且中间不得有多余的空格 ：\n";cin >> exp;
142 
143         int ans = Expression (exp);
144 
145         printf ("%d\n",ans);
146     }
147     return 0;
148 }

 

posted @ 2014-12-03 13:30  无道圣君  阅读(167)  评论(0)    收藏  举报