poj 1028

标准的水题

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <string>
#include <cstdlib>
#include <cstring>
#include <queue>
#include <set>
#include <vector>
#include <map>
#include <algorithm>
#include <cmath>
#include <stack>
#include <stdlib.h>
#include <stdio.h>

#define INF 0x3f3f3f3f
#define LINF 0x3f3f3f3f3f3f3f3f
#define ll long long
#define ull unsigned long long
#define uint unsigned int
#define l(x) x<<1
#define r(x) x<<1|1
#define ms(a,b) memset(a,b,sizeof(a))

using namespace std;

stack<string> sta, st;
string cmd, str;

int main()
{
	sta.push("http://www.acm.org/");
	while (cin >> cmd) {
		if (cmd == "QUIT")           
			break;
		else if (cmd=="VISIT") {    
			cin >> str;
			sta.push(str);
			cout << str << endl;

			while (!st.empty())
				st.pop();
		}
		else if (cmd == "BACK") { 
			if (sta.size() > 1) {
				st.push(sta.top());
				sta.pop();
				cout << sta.top() << endl;
			}
			else
				cout << "Ignored" << endl;
		}
		else if (cmd == "FORWARD") {
			if (!st.empty()) {
				sta.push(st.top());
				cout << st.top() << endl;
				st.pop();
			}
			else
				cout << "Ignored" << endl;
		}
	}

	return 0;
}