LeetCode : valid parentheses

 1 class Solution {
 2 public:
 3     bool isValid(string s) {
 4         
 5         stack<char> istack;
 6         string::iterator p=s.begin();
 7 
 8         while(p!=s.end()){
 9             switch(*p)
10             {
11             case ‘(‘:
12                 istack.push(‘(‘);
13                 break;
14             case ‘[‘:
15                 istack.push(‘[‘);
16                 break;
17             case ‘{‘:
18                 istack.push(‘{‘);
19                 break;
20             case ‘)‘:
21                 if(!istack.empty() && istack.top()==‘(‘)
22                     istack.pop();
23                 else
24                     return false;
25                 break;
26             case ‘]‘:
27                 if(!istack.empty() && istack.top()==‘[‘)
28                     istack.pop();
29                 else
30                     return false;
31                 break;
32             case ‘}‘:
33                 if(!istack.empty() && istack.top()==‘{‘)
34                     istack.pop();
35                 else
36                     return false;
37                 break;
38             default:
39                 break;
40             }
41             p++;
42         }
43         if(istack.empty())
44             return true;
45         else
46             return false;
47     }
48 };