toj 1196 栈的运用（模拟浏览器）

 1 #include <iostream>
 2 #include <string>
 3 #include <stack>
 4 using namespace std;
 5 
 6 stack<string> forward;
 7 stack<string> back;
 8 
 9 int main ()
10 {
11     string cur("http://www.acm.org/"), tmp;
12     while ( cin >> tmp )
13     {
14         if ( tmp == "QUIT" )
15         {
16             break;
17         }
18         else if ( tmp == "BACK" )
19         {
20             if ( back.empty() )
21             {
22                 cout << "Ignored" << endl;
23             }
24             else
25             {
26                 forward.push(cur);
27                 cur = back.top();
28                 back.pop();
29                 cout << cur << endl;
30             }
31         }
32         else if ( tmp == "FORWARD" )
33         {
34             if ( forward.empty() )
35             {
36                 cout << "Ignored" << endl;
37             }
38             else
39             {
40                 back.push(cur);
41                 cur = forward.top();
42                 forward.pop();
43                 cout << cur << endl;
44             }
45         }
46         else if ( tmp == "VISIT" )
47         {
48             back.push(cur);
49             cin >> cur;
50             while ( !forward.empty() )
51             {
52                 forward.pop();
53             }
54             cout << cur << endl;
55         }
56     }
57     return 0;
58 }