First, plz read my source.

#include <iostream>
#include <cstdio>
#include <vector>
#include <map>

using namespace std;

int main()
{
    map <string, int> forum;
    string s;

    while ( getline (cin, s))
    {
        if (s == (string)"tram") forum["tram"]++;
        if (s == (string)"trolleybus") forum["trolleybus"]++;
    }
    if (forum["trolleybus"] > forum["tram"]) cout << "Trolleybus driver" << endl;
    if (forum["trolleybus"] < forum["tram"]) cout << "Tram driver" << endl;
    else cout << "Bus driver" << endl;

    system("pause");
    return 0;
}

Ok. This solution's result is "Compilation error".
One of its :

e8411d95-0fcd-44e7-941f-abd986747ed6(13): error: identifier "getline" is undefined
      while ( getline (cin, s))
              ^

But I've seen FAQs, "getline" just use <iostream>. I don't why but I think my solution is take another error, not a "Compilation error".

Plz explain ! Thank you very much !

P.S : Sorry about my bad English.

add
#include <string>