# Structure

* Basic Definition: A struct is defined using the `struct` keyword, followed by the struct name and a block containing member variables.

  ```cpp
  struct Point {
      int x;
      int y;
  };
  ```
* Creating Instances: You can create instances of a struct like this:

  ```cpp
  Point p1;
  p1.x = 10;
  p1.y = 20;

  // Or using an initializer list (C++11 and later)
  Point p2 = {30, 40};
  ```
* Member Access: Access struct members using the dot (.) operator:

  ```cpp
  std::cout << "p1: (" << p1.x << ", " << p1.y << ")" << std::endl;
  ```
* Functions in Structs: Structs can also contain functions (methods):

  ```cpp
  struct Rectangle {
      int width;
      int height;

      int area() {
          return width * height;
      }
  };
  ```
* Constructors: You can define constructors for initialization:

  ```cpp
  struct Person {
      std::string name;
      int age;

      Person(std::string n, int a) : name(n), age(a) {}
  };

  Person alice("Alice", 30);
  ```
* Default Access Specifier: In a struct, members are public by default (unlike in classes where they're private by default).
* Nested Structs: You can nest structs within other structs:

  ```cpp
  struct Address {
      std::string street;
      std::string city;
  };

  struct Employee {
      std::string name;
      Address workAddress;
  };
  ```
* Pointers to Structs: You can create pointers to structs and access members using the arrow (->) operator:

  ```cpp
  Point* pPtr = &p1;
  std::cout << pPtr->x << ", " << pPtr->y << std::endl;
  ```
* Struct vs Class: The main difference is the default access specifier. Structs are often used for simple data structures, while classes are used for more complex objects with behaviors.
* Memory Alignment: Structs can have padding between members for memory alignment. You can use `#pragma pack` or `__attribute__((packed))` to control this.

Example:

```cpp
#include <iostream>
#include <string>

struct Date {
    int day;
    int month;
    int year;

    Date(int d, int m, int y) : day(d), month(m), year(y) {}

    void display() {
        std::cout << day << "/" << month << "/" << year << std::endl;
    }
};

struct Person {
    std::string name;
    Date birthDate;

    Person(std::string n, Date bd) : name(n), birthDate(bd) {}

    void introduce() {
        std::cout << "Hi, I'm " << name << ". I was born on ";
        birthDate.display();
    }
};

int main() {
    Date bobBirthDate(15, 6, 1990);
    Person bob("Bob", bobBirthDate);

    bob.introduce();

    return 0;
}
```

> Run it [here](https://onecompiler.com/cpp/42kzxu7me).