if(IsPlayerInAnyVehicle(id))
{
new vehicleid=GetPlayerVehicleID(id),
maxseats=GetMaxSeats(vehicleid),
bool:isfull=true;
for(new seat=0; seat <= maxseats; seat++)
{
    if(!IsSeatTaken(vehicleid,seat)) continue;
    PutPlayerInVehicle(id,vehicleid,seat);
    isfull=false;
    break;
}
if(isfull)
{
        SendClientMessage(playerid, COLOR_WARNING, \"(( Nem volt hely a kocsiban, ezért mellé teleportáltál! ))\");
        // ...
}
else
{
     Uzenet(playerid, -1, \"Hozzá teleportáltál: %s! \", SpacedName(Neved(id)));
     // ...
}
}

new vehicleid=GetPlayerVehicleID(id),
    maxseats=GetMaxSeats(GetVehicleModel(vehicleid)),
    bool:isfull=true;