C++ Encapsulation

Why encapsulation matters

When you make data members private and provide public methods to read or change them, you protect your object from being put into an invalid state. Other code cannot reach in and set a value to something nonsensical, because it must go through methods that you wrote and that you can add checks to.

• Better control: you decide exactly how a value can be read or modified.
• Safety: you can validate input before storing it.
• Flexibility: you can change how data is stored internally without breaking code that uses your class.

#include <iostream>
using namespace std;

class Employee {
  private:
    int salary;   // hidden

  public:
    // Setter
    void setSalary(int s) {
      salary = s;
    }
    // Getter
    int getSalary() {
      return salary;
    }
};

int main() {
  Employee emp;
  emp.setSalary(50000);
  cout << "Salary: " << emp.getSalary();
  return 0;
}

The pair of methods above is often called a getter (returns the value) and a setter (changes the value). Because salary is private, they are the only doorway to it, which means the class is fully in charge of that field.

#include <iostream>
using namespace std;

class Thermostat {
  private:
    int temperature;

  public:
    void setTemperature(int t) {
      if (t < 10) t = 10;      // never below 10
      if (t > 30) t = 30;      // never above 30
      temperature = t;
    }
    int getTemperature() {
      return temperature;
    }
};

int main() {
  Thermostat room;
  room.setTemperature(45);            // too high, clamped
  cout << room.getTemperature();      // prints 30
  return 0;
}

As a rule of thumb: keep your data private, expose behavior through public methods, and only add a getter or setter when you genuinely need outside access. Encapsulation is about giving your class a clean, dependable front door.