objects and instances

[sesslit805]

Can someone explain what is an instance of an object?

[gunnerfunner]

adds it to the passengers vector

instead use std::set<Passenger> after overloading operator < for class Passenger, then use the insert method which returns a std::pair<iterator, bool>, the bool being set to true if new element was inserted, false otherwise
http://stackoverflow.com/questions/9586281/set-detect-insertion-failure

[sesslit805]

Also how do I include vectors in all this ?

[JLBorges]

Add a member function to the class Passenger which returns the unique id of he passenger.

Something like:

class Passenger
{
 private:
    Person personInfo; 
    // ...
 public:
    // ...
    std::string passenger_id() const { return personInfo.get_id() ; }
};

Then in FlightReservation::CreateNewPassenger, first check if a passenger with this particular id already exists in the vector of passengers (iterate through the vector to see if there is a match for this id).

[gunnerfunner]

you haven't shown FlightReservation.h but if an instance of this type pertains to a particular flight then the associated container (std::vector or std::set) should be a data-member of this class