POJ 1028 - Web Navigation

#include <cstdio>
#include <iostream>
#include <stack>
#include <string>
using namespace std;

int main()
{
//freopen("input.txt", "r", stdin);
stack<string> stackForward, stackBack;
int i, j;
string now = "http://www.acm.org/", str;
while (cin >> str)
{
if (str[0] == 'Q')
break;
else if (str[0] == 'B')
{
if (stackBack.empty())
cout << "Ignored" << endl;
else
{
stackForward.push(now);
now = stackBack.top();
cout << stackBack.top() << endl;
stackBack.pop();
}
}
else if (str[0] == 'F')
{
if (stackForward.empty())
cout << "Ignored" << endl;
else
{
stackBack.push(now);
now = stackForward.top();
cout << stackForward.top() << endl;
stackForward.pop();
}
}
else if (str[0] == 'V')
{
stackBack.push(now);
cin >> now;
cout << now << endl;
while (!stackForward.empty())
stackForward.pop();
}
}
return 0;
}