Why isn't my class recognizing the iostream class inside my main.cpp although I included iostream?

Question

So I was practicing OOPS and was trying to understand private and public.For this I created a different file in sources folder of my project(btw I am using Code::Blocks) like this:

+--Sources
  +--main.cpp
  +--student.cpp

main.cpp :

#include <iostream>
#include "student.cpp"

using namespace std;

int main(){
    Student s1;

    s1.age = 20;

    s1.rollNo = 101;

    s1.display();

}

student.cpp :

class Student{
public:
    int rollNo;

private:
    int age;

public:
    void display(){
        cout << age << " " << rollNo << endl;

    }
};

Edited student.cpp :

#include <iostream>

class Student{
public:
    int rollNo;

private:
    int age;

public:
    void display(){
        std::cout << age << " " << rollNo << std::endl;

    }
};

And this is giving me the following errors:

error: 'endl' was not declared in this scope
error: 'cout' was not declared in this scope
error: 'int Student::age' is private within this context

From what I understand,first two errors are due to the student.cpp not recognizing iostream headers.Is there different way to work with classes in code::blocks and if not what else can I use?

Also why am I getting third error,since I am trying to access age using a different function(display) which is public inside the Student class?

Answer 1

There are too many issues with the organization of this code that lead you to the problem. Here it is a list of things to fix:

1. Never use naked using namespace std; (outside a well defined scope). Using it "globally" (like you did) breaks encapsulation (in some sense) by changing the meaning of code far away. The puzzling behavior is only one of the consequences.
2. cpp files are never #included. cpps are for implementation and hpps are for declaration (and maybe some implementation).
3. Your student.cpp file should be a student.hpp really
4. student.hpp should have its own "header" dependencies (#include<iostream> in student.hpp)
5. Say std::cout and std::endl, or using std::cout; using std::endl; (at worst using namespace std) but locally.

All above is about style and conventions. Besides that you have syntax error:

1. age should be public according to the desired usage in main.
2. Seems from the comments that your want to protect some internals of the class (like age), in that case you need to make them private, not access them from main, and have a public constructor for the class.

---

Ideally your code should look like this (not tested):

+--Sources
  +--main.cpp
  +--student.hpp

main.cpp :

#include "student.hpp"

using namespace std;

int main(){
    Student s1;

    s1.age = 20;

    s1.rollNo = 101;

    s1.display();

}

student.hpp :

#include <iostream>

class Student{
public:
    int rollNo;
    int age;
private:
    // was int age
public:
    void display(){
        using std::cout;
        cout<< age <<" "<< rollNo <<'\n'; // no need for endl
    }
};

student.cpp is not needed or might be empty.