Scope Resolution

Introduction

The scope resolution operator (::) in C++ is used to define and access something that is outside the current scope.

For example:

#include <iostream>
using namespace std;

class Rectangle {
private:
    int length;
    int breadth;

public:
    // Constructor to initialize length and breadth
    Rectangle(int l, int b) {
        length = l;
        breadth = b;
    }

    // Function to calculate area (declared inside the class)
    int area();

    // Function to calculate perimeter (defined inside the class)
    int perimeter() {
        return 2 * (length + breadth);
    }
};

// Definition of the area function outside the class using scope resolution
int Rectangle::area() {
    return length * breadth;
}

int main() {
    // Create a Rectangle object
    Rectangle rect(10, 5);

    // Call the area function
    cout << "Area of Rectangle: " << rect.area() << endl;

    // Call the perimeter function
    cout << "Perimeter of Rectangle: " << rect.perimeter() << endl;

    return 0;
}

Output:

Area of Rectangle: 50
Perimeter of Rectangle: 30

Explanation:

Step 1: Include the Necessary Header:

#include <iostream>
using namespace std;

• This includes the standard input/output stream library and allows the use of the std namespace for convenience.

Step 2: Class Definition

class Rectangle {
private:
    int length;
    int breadth;

• Private Members: length and breadth are private data members, meaning they can only be accessed within the Rectangle class.

Step 3: Constructor

Rectangle(int l, int b) {
    length = l;
    breadth = b;
}

• Constructor: This constructor initializes the length and breadth when an object of the Rectangle class is created.

Step 4: Function Declarations:

int area();
int perimeter() {
    return 2 * (length + breadth);
}

• area() Function: Declared here but defined outside the class. The function calculates the area of the rectangle.
• perimeter() Function: Defined inside the class. It calculates the perimeter of the rectangle using the formula 2×(length+breadth).

Step 4: Definition of area() Function Using Scope Resolution:

int Rectangle::area() {
    return length * breadth;
}

• Scope Resolution Operator (::): This is used to define the area function outside the class. It tells the compiler that this area function belongs to the Rectangle class.

Step 5: Main Function

int main() {
    Rectangle rect(10, 5);

    cout << "Area of Rectangle: " << rect.area() << endl;
    cout << "Perimeter of Rectangle: " << rect.perimeter() << endl;

    return 0;
}

• Create Object: An object rect of the Rectangle class is created with length = 10 and breadth = 5.
• Call Functions:

rect.area() calculates and prints the area of the rectangle.

rect.perimeter() calculates and prints the perimeter of the rectangle.

Summary:

• Scope Resolution Operator (::): Used to define the area() function outside the class after it has been declared inside the class.
• Constructor: Initializes the object’s length and breadth.
• Member Functions: area() and perimeter() calculate the rectangle’s area and perimeter, respectively.