ddd.cpp

#include "std_lib_facilities.h"

class student {
private:
 int mnr;
public:
 student(int);
 void print(void);
};

student::student(int mnr) { this->mnr = mnr;}
void student::print(void) { cout <<mnr<<endl;}


class group {
private:
 int size;
 vector<student> participants;
public:
 group(void);
 group(student);
 void addStudent(student);
 void listAll();
 int getSize();
 friend group operator+ (group a, group b); };


group::group(void) {}
group::group(student stud) {participants.push_back(stud);}
void group::addStudent(student stud) {participants.push_back(stud);}

void group::listAll()
{
 if(getSize()==0) {throw length_error( "vector is   empty");}
 else {

     for( auto i : participants)
         {cout << i<<endl; }

      }

}

int group::getSize() { return participants.size(); }

group operator+(group a, group b)
 {
   group ab();
   ab.reserve( a.size(), b.size());
   ab.insert(ab.begin(), a.begin(), a.end());
   ab.insert(ab.end(), b.begin(), b.end());

   return ab;


}

int main() {
 group a(student(1234567)), b(student(7654321));
 group myGroup = a + b;
 try {
   myGroup.listAll();
} catch (string error) {
   cerr << error << endl; }
 return 0; }