C++ Classes and Objects

C++ is an object oriented language. A class is a blueprint, and an object is a real thing made from it. A class has data members (variables) and member functions (methods).

#include <iostream>
#include <string>

class Student {
public:
    std::string name;
    int marks = 0;

    void show() const {
        std::cout << name << " scored " << marks << '\n';
    }
};                                       // do not forget this semicolon

int main() {
    Student s1;                          // an object on the stack
    s1.name = "Riya";
    s1.marks = 88;

    Student s2{"Aman", 72};              // aggregate initialization
    s1.show();
    s2.show();
}

Every object has its own copy of the data members. The const after show() means the method does not change the object.

Define a method outside the class

#include <iostream>

class Counter {
public:
    void increment();
    int value() const;
private:
    int count = 0;
};

void Counter::increment() { count++; }              // Class::method
int Counter::value() const { return count; }

int main() {
    Counter c;
    c.increment();
    c.increment();
    std::cout << c.value() << '\n';
}

In real projects the class is declared in a header file (.h) and the methods are defined in a .cpp file.

struct and class

A struct is the same as a class, but its members are public by default, and a class has private by default. Use struct for simple data, and class for things with behavior.

#include <iostream>

struct Point {
    int x = 0;
    int y = 0;
};

int main() {
    Point p{3, 4};
    std::cout << p.x + p.y << '\n';
}

Objects and pointers

#include <iostream>
#include <memory>
#include <string>

struct Pet {
    std::string name;
    void speak() const { std::cout << name << " says hi\n"; }
};

int main() {
    Pet a{"Tommy"};
    a.speak();                                    // dot for an object

    auto b = std::make_unique<Pet>(Pet{"Kitty"});
    b->speak();                                   // arrow for a pointer
}

• Previous Page
• Next Page

---

Exercises & Assignments
No Content Found.

Interview Questions & Answers
No Content Found.