Difference Between Structure and Class in C++

If you’re new to programming, learning C++ can seem intimidating. But don’t worry  you’re not alone! You might notice that C++ has two types of data structures (structs) and classes (classes).At first glance, they might seem similar. After all, both can contain variables and functions. It’s important to understand how they behave under the hood so that you can write clean, professional C++ code.

What is a Structure in C++?

A structure (declared using struct) is a simple way to group related data together. Think of it like a file folder it keeps different but related papers (data) in one place. In a struct, all members are public by default meaning they can be accessed from anywhere.

In C++, a structure can hold variables (called data members) and even simple functions.

Real-life example:

Imagine a student record. Each student has a:

• Roll number
• Name
• Marks

All these pieces of information can be grouped using a struct.

#include <iostream> // This allows us to use input/output functions like cout
using namespace std; // So we don’t have to write std:: before every C++ keyword

// Define a structure named 'Student' to group related data
struct Student {
    int roll;        // Variable to store the student's roll number
    string name;     // Variable to store the student's name
    float marks;     // Variable to store the student's marks

    // A function inside the struct to display the student's details
    void display() {
        // Print the roll number
        cout << "Roll: " << roll << endl;

        // Print the name
        cout << "Name: " << name << endl;

        // Print the marks
        cout << "Marks: " << marks << endl;
    }
};

int main() {
    Student s1; // Create an object 's1' of the structure 'Student'
    // Assign values to the s1 object’s variables
    s1.roll = 1;              // Assign roll number 1
    s1.name = "John";         // Assign name "John"
    s1.marks = 95.5;          // Assign marks 95.5
    s1.display(); // Call the function to print the student’s details
    return 0; // Indicate that the program ended successfully
}

Output:

Roll: 1
Name: John
Marks: 95.5

What is a Class in C++?

A class is like a more secure structure. It also groups data and functions, but gives you control over who can access the data. Classes follow the principles of Object-Oriented Programming (OOP) like encapsulation, abstraction, inheritance, and polymorphism.

In a class, all members are private by default, meaning they can’t be accessed directly from outside the class. You have to use functions to get or set data.

Real-life example:

Think of a bank locker:

• You can store valuable items (data).
• Only authorized people (functions) can access it.
• Outsiders can’t directly open the locker — they need permission.

Simple Syntax and Example:

#include <iostream> // Allows us to use input/output like cout
using namespace std; // So we don't need to write std:: before every C++ keyword

// Define a class named 'Student'
class Student {
    // These are private variables by default (only accessible inside the class)
    int roll;        // To store roll number
    string name;     // To store name
    float marks;     // To store marks

public:
    // This function lets us assign values to the private variables
    void setDetails(int r, string n, float m) {
        roll = r;     // Set roll number
        name = n;     // Set name
        marks = m;    // Set marks
    }

    // This function prints the student’s details
    void display() {
        cout << "Roll: " << roll << endl;   // Print roll number
        cout << "Name: " << name << endl;   // Print name
        cout << "Marks: " << marks << endl; // Print marks
    }
};

int main() {
    Student s1; // Create a student object named 's1'

    // Set details for student using the function
    s1.setDetails(2, "Alice", 89.5);

    // Show the stored details on screen
    s1.display();

    return 0; // Program ends successfully
}

Output:

Roll: 2
Name: Alice
Marks: 89.5

Key Differences

Struct in C++

1. Default Access: Public
   
2. Inheritance Type: Public by default
   
3. Usage: Ideal for simple data containers (e.g., coordinates, RGB values, dates).
   
4. Encapsulation: Weak or no data hiding  members can be accessed directly.
   
5. Flexibility: Less secure, no strict OOP rules.
   
6. Syntax: Very easy and beginner-friendly.
   
7. Best Use Case: When you just want to group variables without logic or security.

 Class in C++

1. Default Access: Private
   
2. Inheritance Type: Private by default.
   
3. Usage: Ideal for secure and complex object-oriented models.
   
4. Encapsulation: Strong members are hidden unless explicitly made public.
   
5. Flexibility: More secure, supports full object-oriented features like inheritance, polymorphism, abstraction.
   
6. Syntax: Slightly more complex due to access specifiers and functions.
   
7. Best Use Case: When you need to hide internal data and control how it’s accessed. 

When to Use What?

 Use struct when:

• You are working with simple data models.
• You want all variables to be public.
• Example: Point, Date, etc.

 Use class when:

• You want to hide details from outside.
• You are designing software with user interaction, business logic, etc.
• Example: Bank Account, Employee, Vehicle, etc.