C++ Classes Notes

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1. What are Classes?

📌 Key Idea: Classes group data (variables) and functionality (methods) into reusable blueprints.

• Purpose: Organize code, model real-world entities (e.g., Player, Car).
• Object: An instance of a class (e.g., Player player1;).

Example Without Classes (Messy Variables):

int playerX, playerY; // Position  
int playerSpeed = 2;  
void move(int& x, int& y, int speed) { /* ... */ }  

With Classes (Organized):

class Player {  
public:  
    int x, y, speed;  
    void move(int xa, int ya) {  
        x += xa * speed;  
        y += ya * speed;  
    }  
};  

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2. Creating a Class

Syntax:

class ClassName {  
    // Data (variables) and methods (functions)  
};  

Example:

class Player {  
public:  
    int x = 0, y = 0;  
    int speed = 2;  
};  

• Instantiate an object:

  Player player1;  
  player1.x = 5; // Access member variables  
  

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3. Visibility: Public vs. Private

• public: Accessible outside the class.
• private (default): Accessible only inside the class.

Example:

class Player {  
public:  // Accessible anywhere  
    int x, y;  
private: // Accessible only inside Player  
    int health = 100;  
};  

• Error: player1.health = 50; ❌ (private member).
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4. Methods (Class Functions)

Methods are functions inside a class that operate on the class’s data.

Standalone Function vs. Class Method:

// Standalone function (before classes)  
void move(Player& player, int xa, int ya) {  
    player.x += xa * player.speed;  
}  

// Class method (cleaner!)  
class Player {  
public:  
    void move(int xa, int ya) {  
        x += xa * speed; // Direct access to x, speed  
    }  
};  

Usage:

Player player1;  
player1.move(1, -1); // Moves player1  

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5. Key Takeaways

1. Classes group related data + logic: Avoid scattered variables.
2. Objects are instances: Player player1; creates a Player object.
3. Encapsulation: Use public/private to control access.
4. Methods simplify code: Replace standalone functions with class methods.

Remember: Classes are syntactic sugar for code organization—they don’t add new functionality, just structure!

💡 Pro Tip: Use classes to model entities in your code (e.g., Enemy, Inventory) for cleaner, maintainable projects!