3-6 中缀表达式转换成后缀表达式

 1 #include <iostream>
 2 #include <cctype>
 3 #include <stack>
 4 using namespace std;
 5 
 6 int getPriority(char ch)
 7 {
 8     int priority = 0;
 9     switch(ch)
10     {
11         case ‘+‘:
12             priority = 1;
13             break;
14         case ‘-‘:
15             priority = 1;
16             break;
17         case ‘*‘:
18             priority = 2;
19             break;
20         case ‘/‘:
21             priority = 2;
22             break;
23         case ‘(‘:
24             priority = 3;
25             break;
26         default:
27             priority = 0;
28             break;
29     }
30     return priority;
31 }
32 
33 
34 int main()
35 {
36     std::stack<char> S;
37     char ch;
38     cin >> ch;
39     while (ch != ‘#‘)
40     {
41         while (isdigit(ch))
42         {
43             cout << ch;
44             cin >> ch;
45             if(!isdigit(ch))        //ch 不是数字且不是‘#‘， 表示完成了一个整型数据的输入，此时打印一个空格
46                 cout << " ";
47             
48 
49         }
50         if (ch == ‘#‘)
51             break;
52         if (ch == ‘)‘)                    //如果读入的字符是‘）‘，那么当栈顶元素不是‘（’时，一直输出栈顶元素
53         {
54             while (S.top() != ‘(‘)
55             {
56                 cout  << S.top()<< " ";
57                 S.pop();
58             }
59             S.pop();
60         }
61         else     //正常情况，将ch和栈顶字符比较优先级
62         {
63             while (!S.empty() && S.top() != ‘(‘ && getPriority(S.top()) >= getPriority(ch))
64             {
65                 cout << S.top()<< " " ;
66                 S.pop();
67             }
68             S.push(ch);
69 
70         }cin >> ch;
71     }
72 
73     while (!S.empty())
74     {
75         cout << S.top();
76         S.pop();
77         if (!S.empty())
78             cout << " ";
79     }
80 
81     return 0;
82 }