exited with non-zero status

I am trying to write some classes and test them manually using c++ 11 in order to understand how to code CPP, but i somehow get this error "exited with non-zero status". I am new to CPP and i do not understand where i might be going wrong. I would like to maintain shallow copy. Can someone please let me know where i am wrong? Or how to modify this to make it better?

This is what i have done:

#include <cctype>
#include <iostream>

using namespace std;

class User {
  public:
  enum class Status { UNKNOWN, ONLINE, OFFLINE};

    string *userName;
    string *userUri;
    Status *userStatus;

    public:
    User () { 
      userName = new string;
      userUri = new string;
      *userName = ""; *userUri = ""; *userStatus = Status::UNKNOWN;
  }

    User (string);

    User (string, string);

    bool isNull() {
        return (userUri->empty() || userName->compare("") == 0);
    }

  friend bool operator==(User& user1, User& user2) { 
    return user1.uri().compare(user2.uri()) == 0;
  }

  User operator=(User& user) {
    userUri = user.userUri;
    userName = user.userName;
    userStatus = user.userStatus;
  }

    string uri() { return *userUri; }

    string name() { return *userName; }

    Status status() { return *userStatus; }

    void setName(string);

    void setStatus(User::Status);

    ~User();
};

User::User(string uri)  {
  *userUri = uri;
}

User::User (string uri, string name) {
  *userUri = uri;
  *userName = name;
}

void User::setName(string name) {
  if (isNull()) {
    return;
  }
  *userName = name;
}

void User::setStatus(User::Status status) {
  if (isNull()) {
    return;
  }
  *userStatus = status;
}

User::~User() {
    delete userName, userUri, userStatus;
    userName = NULL;
    userUri = NULL;
    userStatus = NULL;
}

int main() {
    User u, u1;
    cout << u.isNull() << "\n";
    cout << (u.uri().compare("") > 0) << endl;
    cout << (u.name().compare("") > 0)<< endl;
    cout << (u.status() == User::Status::UNKNOWN) << endl;
    cout << (u == u1) << endl;
    u.setName("dhara");
    cout << (u.name().compare("") == 0) << endl;
    u.setStatus(User::Status::ONLINE);
    cout << (u.status() == User::Status::UNKNOWN) << endl;

    User u2("a@a.com","Robert");
    User u3 = u2;
    u3.setName("dhara");

    cout << u3.uri() << endl;
    cout << u2.name() << endl;
    return 0;
}