Question

I need help with something which I believe is simple. I can assign a student to a project. But when I delete the project, the student is still keeping the project name. I’m thinking of just renaming it back to “None” but I have no idea on how to do that. Help?

Edit
map<int, Student> mstore and vector<int> storeid added.

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
#include <map>
using namespace std;
class Human {
public:
    virtual void print() const = 0;
};

class Student : public Human {
protected:
    string studname;
    int studId;
    string project;
public:

    Student();
    Student (string studname, int studId) : studname("Unknown"), studId(0), project("None") 
    {
        cout << "A student is created: Name = " << studname
         << ". Id = " << studId << endl;
    }

    virtual void print() const {
    cout << "Name = " << studname << ". Id = " << studId << ". Project = " << project <<endl; }

    void setSName (string sname) { studname = sname; }
    void setSID (int sID) { studId = sID; }
    void printStudentInfo() const;
    void printStudentInfoline() const;
};

void Student::printStudentInfo() const
{
    cout << "\nStudent name: " << studname << endl;
    cout << "Student ID: " << studId << endl;
    cout << "Project: " << project << endl;
}

void Student::printStudentInfoline() const
{
    cout << studId << ", " << studname << ", " << project << endl;
}

class Project {
protected:
    string projname;

public:
    vector <Student> students;
    vector <int> storeid;

    Project (string projname) : projname(projname) { cout << "Project " << projname << " created" << endl;}

    void setPName (string projname) { this->projname = projname; }

    void add (int& sid) 
    {
        //student.setProject (projname);
        storeid.push_back(sid);
    }

    int returnid(int& a)
    {   
        return storeid[a]; 
    }

    int returnsize()
    {   return storeid.size(); }

    void printproj() const {
        cout << endl << projname << " list: \n";
        cout << "Student(s) : " << endl;
        for (int i = 0; i < storeid.size(); i++){
            cout << storeid[i] << endl;
        }
    }

    void printprojname() const {
    cout << projname << endl;
    }


};

int main() {
string StudentName;
string ProjectName;

int Studentid;

Student *s1;
Project *p1;

vector<Student> store;
vector<Project> projstore;
map<int, Student> mstore;


map<int, Student>::const_iterator itr;
    for (int n=0; n<3; n++) //loop to create 3 students
   { 
    cout <<"Enter name : ";
    getline(cin, StudentName);
    cout <<"Enter  ID : ";
    cin >> Studentid;

    s1 = new Student(StudentName, Studentid);
    s1->setSName(StudentName);
    s1->setSID(Studentid);
    store.push_back(*s1);
    mstore.insert(make_pair(Studentid, *s1));
    cin.get();
    }
    //print map
    for(itr=mstore.begin(); itr!=mstore.end() ;++itr)
    itr->second.printStudentInfo();

    //itr=mstore.begin()+2;
    //itr.print();




cout << "Enter project name: ";
getline(cin, ProjectName);

p1 = new Project(ProjectName);
p1->setPName(ProjectName);

 //Assigning student to project
    cout << endl;
    cout << "How many students? :" ;

    int y;
    cin >> y;
    for ( int i = 0; i < y; i++){
    cout << "Who would you like to add to this project?" << endl;
    int x = 1;

    for(itr=mstore.begin(); itr!=mstore.end() ;++itr)
    itr->second.printStudentInfoline();

    int insID;
    cout << "Enter ID number: ";
    cin >> insID;
    p1->add(insID);

    /*
    for ( it = store.begin(); it != store.end(); ++it ) {
        // For each friend, print out their info

    cout << x << ". ";
          it->printStudentInfoline();
    x++;

    }
    x = 1;  
    int insS;
    cout << "Enter number: ";
    cin >> insS;
    p1->add(store[(insS-1)]);   //stores selected student into the object
    */

    cout << "\nAdding Student done\n" << endl;
    }
    projstore.push_back(*p1);

    //Mstore finds for related ids and displays them accordingly
cout << "print project"<< endl;
    vector<Project>::iterator pt;
    for ( pt = projstore.begin(); pt != projstore.end(); ++pt ) {
        pt->returnsize();
        for (int i=0; i <pt->returnsize(); i++){
        cout << pt->returnid(i) << endl;

        itr=mstore.find(pt->returnid(i));

        itr->second.printStudentInfo();
        }            
    }


    cout << endl;
    cout << "Deleting project" << endl;
    cout << "What would you like to remove?" << endl;
    int x = 1;

    //storeid will display ids. How do I link them to `store` map?
    for ( pt = projstore.begin(); pt != projstore.end(); ++pt ) {
      cout << x << ". ";
      pt->printprojname();
      x++;
    }


    //Now to delete the selected project
    int delP;
    cout << "Enter number: ";
    cin >> delP;
    cin.ignore();
    system("pause");
    projstore.erase(projstore.begin()+delP-1);

// Students

cout << "\n Current students" << endl;
for(itr=mstore.begin(); itr!=mstore.end() ;++itr)
    itr->second.printStudentInfo();

}

Answer 1

Look at how you add a Student to a Project:

void add (Student& student)
{
  student.setProject (projname);
  students.push_back (student);    // <-- AHA!
}

First you assign the Project name to the Student, then the Project stores a copy of the Student. After that, the Project has no link to the original Student, and can’t inform him/her of its own demise when the time comes.

You’ll have to rethink this design; there are three major options: 1) the Students can look up their respective Projects in the store, 2) the Project can look up its Students in the students vector, or 3) the Project owns the Students (in which case they should probably be GraduateStudents).

EDIT:
If that’s the way you want to do it, use map<int, Student> store to store the Students, using ID number as an index. Then a Project can have a vector<int> (or set<int>) of student ID numbers. It can look Students up in the store with ease.

EDIT:
To print out the entire collection of students:

for(map<int, Student>::const_iterator itr=store.begin(); itr!=store.end() ;++itr)
  itr->second.print();

EDIT:
If the Project has a vector<int> of student ID numbers, then what argument do you think Project::add(?) should take?

EDIT:
The Project can act on a Student by means of the student ID number and access to mstore:

// in Project:
mstore[id].whatever()

EDIT:
Sometimes asking the right question — or in this case, phrasing the question correctly — is half the battle. ‘Now how do I change “None” to the inserted project name?’ A better way to put it is ‘How does the Project change one of its Student’s project from “None” to projname?’ Once you put it that way, the answer is almost obvious:

// in Project:
mstore[id].setSProject(projname);

Note that Student does not yet have setSProject(string), you’ll have to add it. Also, note that this solution is not ideal since 1) anybody can change a Student’s project, and 2) a Student’s project need not actually be the name of a real Project. There is more than one way to deal with these problems.