【栈】一个简答的四则运算计算器的实现

 1 char * InfixToPostfix(char *s) {
 2     if (s == NULL) return NULL;
 3     stack<char> st;
 4     stack<char> post;
 5 
 6     char *p = s;
 7     int priority[256] = {0}; //设置运算符优先级
 8     priority[‘+‘] = 0;
 9     priority[‘-‘] = 0;
10     priority[‘*‘] = 1;
11     priority[‘/‘] = 1;
12     priority[‘(‘] = -1;
13 
14 
15     while (*p != ‘\0‘) {
16         if (*p >= ‘0‘ && *p <= ‘9‘) {
17             post.push(*p++);
18         } else if (*p == ‘(‘) {
19             st.push(*p++);
20         } else if (*p == ‘)‘) {
21             while (!st.empty() && st.top() != ‘(‘) {
22                 post.push(st.top());
23                 st.pop();
24             }
25             st.pop(); //‘（’出栈
26             ++p;
27         } else {
28             while (!st.empty() && priority[st.top()] >= priority[*p]) {
29                 post.push(st.top());
30                 st.pop();
31             }
32             st.push(*p++);
33         }
34     }
35 
36     while (!st.empty()) {
37         post.push(st.top());
38         st.pop();
39     }
40 
41     while (!post.empty()) {
42         st.push(post.top());
43         post.pop();
44     }
45 
46     int len = strlen(s);
47     char *res = new char[len + 1];
48     int i = 0;
49     while (!st.empty()) {
50         res[i++] = st.top();
51         st.pop();
52     }
53     res[i] = ‘\0‘;
54 
55     return res;
56 }
57 
58 int BinaryComp(int a, int b, char c) {
59     switch (c) {
60     case ‘*‘:
61         return a * b;
62         break;
63     case ‘+‘:
64         return a + b;
65         break;
66     case ‘-‘:
67         return a - b;
68         break;
69     case ‘/‘:
70         return a /b;
71         break;
72     default:
73         break;
74     }
75 }
76 
77 int CalCul(char *s) {
78     if (s == NULL)
79         return 0;
80     stack<int> st;
81     while (*s != ‘\0‘) {
82         if (*s >= ‘0‘ && *s <=‘9‘) {
83             st.push(*s - ‘0‘);
84             ++s;
85         } else {
86             int a = st.top();
87             st.pop();
88             int b = st.top();
89             st.pop();
90             int res = BinaryComp(a, b, *s);
91             s++;
92             st.push(res);
93         }
94     }
95 
96     return st.top();
97 }