Defining member functions

🔷 What Are Member Functions?

Member functions are functions that are defined inside a class and can access the data members (variables) of that class. They define the behavior of the objects created from the class.

Member functions can be:

• Defined inside the class
• Defined outside the class using the scope resolution operator ::

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🔷 Syntax: Defining Member Functions

✅ Inside the Class (Inline Definition)

class Example {
public:
    void display() {
        cout << "Hello from inside the class!" << endl;
    }
};

✅ Outside the Class (Using Scope Resolution Operator ::)

class Example {
public:
    void display();  // Function declaration inside class
};

void Example::display() {  // Function definition outside class
    cout << "Hello from outside the class!" << endl;
}

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🔷 When to Define Inside vs Outside

Inside Class	Outside Class
Automatically treated as inline	Normal function, not inline by default
Suitable for small/simple functions	Suitable for large/complex functions
Keeps all code in one place	Helps keep class definition clean and short

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🔷 Example: Defining Member Functions (Both Ways)

#include <iostream>
using namespace std;

class Student {
private:
    int rollNo;
    float marks;

public:
    void setData(int r, float m); // Declared inside

    void display() {  // Defined inside (inline)
        cout << "Roll No: " << rollNo << endl;
        cout << "Marks: " << marks << endl;
    }
};

// Defined outside using scope resolution operator
void Student::setData(int r, float m) {
    rollNo = r;
    marks = m;
}

int main() {
    Student s1;
    s1.setData(101, 95.5);
    s1.display();
    return 0;
}

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🔷 Key Points

1. Access: Member functions can directly access both private and public data members.
2. Scope Resolution Operator ::: Used to define functions outside the class.
3. Encapsulation: Functions operate on the data, ensuring safe access and modification.

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🔷 Benefits of Using Member Functions

• Maintains code reusability.
• Promotes data abstraction and modularity.
• Functions are tied to the class they operate on — this improves organization and readability.

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🔷 Diagram (Text Format)

Class: Student
-----------------------------
| - rollNo : int             |
| - marks : float            |
| + setData(int, float)      | --> defined outside
| + display()                | --> defined inside
-----------------------------

Object: s1
s1.setData(101, 95.5)
s1.display()

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🔷 Summary

• Member functions define how an object behaves.
• They can be defined inside (inline) or outside (with ::) the class.
• They improve encapsulation, data protection, and object-oriented structure.