c++ program outputs series of numbers instead of cout - c++

Question

My current assignment is to create a simple
Student Class that takes the
first name
last name
student ID number
from an object and outputs the name as a single string and his/her ID number. The program also has to count every student and output the total number of students. In this program I'm given 4 students.
I've created the program, given below. Everything compiles correctly and runs but my output is strange. Instead of giving me the students' ID and name, it gives me the number "-858993460". I have no idea why my program's doing this and a long search on the internet hasn't helped me much.
Student.h
#include <iostream>
#include <string>
using namespace std;
class Student
{
private:
string firstName;
string lastName;
int id;
string name;
public:
static int numberOfStudents;
Student();
Student(string theFirstName, string theLastName, int theID);
string getName();
int getID();
};
Student.cpp
#include "Student.h"
#include <iostream>
#include <string>
using namespace std;
//initialize numberOfStudents to 0
int Student::numberOfStudents = 0;
//initialize default constructor
Student::Student()
{
numberOfStudents++;
}
//initialize overloaded constructor
Student::Student(string theFirstName, string theLastName, int theID)
{
theFirstName = firstName;
theLastName = lastName;
theID = id;
numberOfStudents++;
}
//getName
string Student::getName()
{
return firstName += lastName;
}
//getID
int Student::getID()
{
return id;
}
main.cpp(this is my driver file)
#include "Student.h"
#include <iostream>
#include <string>
using namespace std;
int main()
{
Student st1("Hakan", "Haberdar", 1234), st2("Charu", "Hans", 2345), st3("Tarikul", "Islam", 5442), st4;
cout << "We created " << Student::numberOfStudents<<" student objects." << endl;
cout << st1.getID()<<" "<<st1.getName()<<endl;
cout << st2.getID()<<" "<<st2.getName()<<endl;
cout << st3.getID()<<" "<<st3.getName()<<endl;
cout << st4.getID()<<" "<<st3.getName()<<endl;
system("pause");
};
This is what my output is supposed to look like:
We created 4 student objects.
1234 Hakan Haberdar
2345 Charu Hans
5442 Tarikul Islam
0
This is what my output instead looks like:
We created 4 student objects.
-858993460
-858993460
-858993460
-858993460
I think my problem has something to do with my getName() function, but I'm not sure and I don't know what to try.

Answer 1

Student::Student(string theFirstName, string theLastName, int theID)
{
theFirstName = firstName;
theLastName = lastName;
theID = id;
numberOfStudents++;
}
Your assignments are the wrong way round. You're assigning the as yet uninitialised members to the arguments. Instead you should have:
Student::Student(string theFirstName, string theLastName, int theID)
{
firstName = theFirstName;
lastName = theLastName;
id = theID;
numberOfStudents++;
}
This mistake would have been avoided if you had used a member initialization list instead:
Student::Student(string theFirstName, string theLastName, int theID)
: firstName(theFirstName), lastName(theLastName), id(theID)
{
numberOfStudents++;
}

Answer 2

Not sure if the following is the reason for your issues, but it does seem wrong...
return firstName += lastName;
What this does is modifies firstname by appending last name to it, then returning modified string.
I think you meant to do something like
return firstName << ' ' << lastName;

Answer 3

Change your code to.
Student::Student(string theFirstName, string theLastName, int theID)
{
firstName = theFirstName;
lastName = theLastName;
id = theID;
numberOfStudents++;
}
Your code returning the value of id! which is not initialized.
So the code will return garbage.