Light OJ -- 1113(Discover the Web)

To learn stack(In Bangla)
http://www.shafaetsplanet.com/?p=2342
In english:https://www.geeksforgeeks.org/stack-in-cpp-stl/
Learn function:https://www.cplusplus.com/reference/stack/stack/

///Bismillahir Rahmanir Rahim
///Author:Tanvir Ahmmad
///CSE,Islamic University,Bangladesh

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<string>
#include<cstring>
#include<sstream>
#include<cmath>
#include<cstring>
#include<vector>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<vector>
#include<iterator>
#include <functional> ///sort(arr,arr+n,greater<int>()) for decrement of array
/*every external angle sum=360 degree
  angle find using polygon hand(n) ((n-2)*180)/n*/
///Floor[Log(b)  N] + 1 = the number of digits when any number is represented in base b
using namespace std;
typedef long long ll;
int main()
{
    int tst,ca=1;
    scanf("%d",&tst);
    while(tst--)
    {
        printf("Case %d:\n",ca++);
        stack<string>back_stk,front_stk;
        string str,cur="http://www.lightoj.com/";
        while(1)
        {
            cin>>str;
            if(str=="QUIT") break;
            else if(str=="VISIT")
            {
                cin>>str;
                back_stk.push(cur);
                cur=str;
                while(!front_stk.empty()) front_stk.pop();
                cout<<cur<<endl;
            }
            else if(str=="BACK")
            {
                if(cur=="http://www.lightoj.com/") printf("Ignored\n");
                else
                {
                    front_stk.push(cur);
                    cur=back_stk.top();
                    back_stk.pop();
                    cout<<cur<<endl;
                }
            }
            else if(str=="FORWARD")
            {
                if(front_stk.size()==0) printf("Ignored\n");
                else
                {
                    back_stk.push(cur);
                    cur=front_stk.top();
                    front_stk.pop();
                    cout<<cur<<endl;
                }
            }
        }
    }
    return 0;
}

///Alhamdulillah 
Problem Link:https://lightoj.com/problem/discover-the-web