C++ Class Methods

Types of Methods

int getAge() {
    return age;
}

void setAge(int newAge) {
    age = newAge;
}

void displayInfo() {
    cout << name << endl;
}

double calculateArea() {
    return length * width;
}

🔹 Method Definition Inside Class

Defining methods directly inside a class keeps implementation close to the declaration, enhancing readability for small classes. This inline approach is common for simple getters, setters, or straightforward behaviors. However, for larger or more complex methods, it can clutter the class interface, making the definition harder to read and maintain compared to external definitions.

#include <iostream>
#include <string>
using namespace std;

class Student {
public:
    string name;
    int age;
    double gpa;
    
    // Method defined inside class
    void introduce() {
        cout << "Hi, I'm " << name << endl;
        cout << "I'm " << age << " years old" << endl;
    }
    
    // Method with return value
    string getGrade() {
        if (gpa >= 3.5) return "A";
        else if (gpa >= 3.0) return "B";
        else if (gpa >= 2.5) return "C";
        else return "D";
    }
    
    // Method with parameters
    void updateGPA(double newGPA) {
        gpa = newGPA;
        cout << "GPA updated to: " << gpa << endl;
    }
};

🔹 Method Definition Outside Class

Defining methods outside the class using the scope resolution operator separates interface from implementation. This practice results in a cleaner class header, improves code organization, and makes the class easier to read and maintain. It is especially beneficial in large projects and when method implementations are lengthy or complex.

class Circle {
public:
    double radius;
    
    // Method declarations
    double calculateArea();
    double calculateCircumference();
    void displayInfo();
};

// Method definitions outside class
double Circle::calculateArea() {
    return 3.14159 * radius * radius;
}

double Circle::calculateCircumference() {
    return 2 * 3.14159 * radius;
}

void Circle::displayInfo() {
    cout << "Circle with radius: " << radius << endl;
    cout << "Area: " << calculateArea() << endl;
    cout << "Circumference: " << calculateCircumference() << endl;
}

🔹 Complete Example with Methods

A practical class example integrates various method types to model real-world entities like a bank account. It typically includes constructors for initialization, public methods for operations like deposit() and withdraw(), private helper methods for internal logic, and perhaps a destructor. This demonstrates how methods collaborate to encapsulate behavior and data securely.

#include <iostream>
#include <string>
using namespace std;

class BankAccount {
private:
    string accountNumber;
    double balance;
    
public:
    // Constructor-like method
    void initialize(string accNum, double initialBalance) {
        accountNumber = accNum;
        balance = initialBalance;
    }
    
    // Accessor methods (getters)
    string getAccountNumber() {
        return accountNumber;
    }
    
    double getBalance() {
        return balance;
    }
    
    // Mutator methods with validation
    void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
            cout << "Deposited: $" << amount << endl;
        } else {
            cout << "Invalid deposit amount!" << endl;
        }
    }
    
    bool withdraw(double amount) {
        if (amount > 0 && amount <= balance) {
            balance -= amount;
            cout << "Withdrawn: $" << amount << endl;
            return true;
        } else {
            cout << "Invalid withdrawal!" << endl;
            return false;
        }
    }
    
    // Utility method
    void displayAccountInfo() {
        cout << "Account: " << accountNumber << endl;
        cout << "Balance: $" << balance << endl;
    }
};

int main() {
    BankAccount account;
    
    account.initialize("12345", 1000.0);
    account.displayAccountInfo();
    
    account.deposit(500.0);
    account.withdraw(200.0);
    account.displayAccountInfo();
    
    return 0;
}