C++ - User Defined Data Types

User-Defined Data Types in C++

C++ provides the ability to define custom data types using various mechanisms. These user-defined data types allow programmers to design complex data structures to suit the needs of the application. The primary ways to define user-defined data types in C++ are:

• struct: Defines a structure that groups different data types under one name.
• class: Defines a class which is similar to a structure but with additional features like encapsulation, inheritance, and polymorphism.
• enum: Defines an enumeration, which is a set of named integer constants.
• typedef: Provides an alias for existing data types to make them easier to manage.
• using: Similar to typedef, used to create an alias for existing data types in modern C++.

1. struct - Structure

A struct in C++ is a user-defined data type that allows you to combine data of different types into a single unit. It is similar to a class but does not have access control (private or public members) by default.

Syntax

struct  {
     ;
     ;
    ...
};

You can create a structure by declaring it and then instantiating it as a variable:

Example

#include 
using namespace std;

struct Person {
    string name;
    int age;
};

int main() {
    Person person1;  // Declare a variable of type 'Person'
    person1.name = "John";  // Initialize the 'name' field
    person1.age = 25;  // Initialize the 'age' field
    
    cout << "Name: " << person1.name << endl;
    cout << "Age: " << person1.age << endl;

    return 0;
}

2. class - Class

A class in C++ is a more advanced user-defined data type that extends the functionality of a structure by supporting features such as encapsulation, inheritance, and polymorphism.

A class can have access control keywords such as private, public, and protected that determine the visibility and accessibility of its members.

Syntax

class  {
    :
     ;
     ();
    ...
};

Here's an example of defining and using a class in C++:

Example

#include 
using namespace std;

class Car {
    public:
        string brand;
        int year;

        void display() {
            cout << "Brand: " << brand << ", Year: " << year << endl;
        }
};

int main() {
    Car car1;  // Declare a variable of type 'Car'
    car1.brand = "Toyota";  // Initialize the 'brand' field
    car1.year = 2020;  // Initialize the 'year' field
    
    car1.display();  // Call the display function

    return 0;
}

3. enum - Enumeration

An enum in C++ is a user-defined data type that consists of a set of named integer constants. Enums make code more readable and easier to maintain by using meaningful names instead of raw numeric values.

Syntax

enum  {
     = ,
     = ,
    ...
};

By default, the first constant of an enum is assigned the value 0, and each subsequent constant is incremented by 1 unless otherwise specified.

Example

#include 
using namespace std;

enum Day { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };

int main() {
    Day today = Wednesday;  // Declare and initialize an enum variable
    cout << "Day: " << today << endl;  // Output: Day: 3
    return 0;
}

4. typedef - Type Definition

The typedef keyword in C++ is used to create a new name (alias) for an existing data type. This can be useful when you need to simplify complex data type names or create more readable code.

Syntax

typedef  ;

Example

#include 
using namespace std;

typedef unsigned long ulong;  // Define an alias 'ulong' for 'unsigned long'

int main() {
    ulong population = 7500000000;  // Use the alias 'ulong'
    cout << "Population: " << population << endl;
    return 0;
}

5. using - Alias Declaration

In modern C++, the using keyword can be used as an alternative to typedef to create type aliases. The using syntax is more flexible and easier to read compared to typedef.

Syntax

using  = ;

Example

#include 
using namespace std;

using ulong = unsigned long;  // Define an alias 'ulong' for 'unsigned long'

int main() {
    ulong population = 7500000000;  // Use the alias 'ulong'
    cout << "Population: " << population << endl;
    return 0;
}