void validate(const TaskManager& tasks, const ItemManager& items, std::ostream& os){
auto taskEnd = tasks.cend();
auto itemEnd = items.cend();
const int EQUAL = 0;
bool isAvailable;
// enumerate all tiems
for (auto item = items.cbegin(); item != itemEnd; ++item) {
isAvailable = false;
// enumerate all tasks, compare each task with item destination
for (auto singleTask = tasks.cbegin(); singleTask != taskEnd; ++singleTask) {
if((item->getDestination()).compare(singleTask->getName()) == EQUAL){
isAvailable = true;
break;
}
}
if (isAvailable == false) {
os << item->getDestination() << " is unavailable\n";
}
}
}
