Structures

Structures allow developers to create their own types ("user-defined" types) to aggregate data relevant to their needs.

For example, a user might define a Rectangle structure to hold data about rectangles used in a program.

struct Rectangle {
  float length;
  float width;
};

Types

Every C++ variable is defined with a type.

int value;
Rectangle rectangle;
Sphere earth;

In this example, the "type" of value is int. Furthermore, rectangle is "of type" Rectangle, and earth has type Sphere.

Fundamental Types

C++ includes fundamental types, such as int and float. These fundamental types are sometimes called "primitives".

The Standard Library [includes additional types](, such as std::size_t and std::string.

User-Defined Types

Structures are "user-defined" types. Structures are a way for programmers to create types that aggregate and store data in way that makes sense in the context of a program.

For example, C++ does not have a fundamental type for storing a date. (The Standard Library does include types related to time, which can be converted to dates.)

A programmer might desire to create a type to store a date.

Consider the following example:

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

The code above creates a structure containing three "member variables" of type int: day, month and year.

If you then create an "instance" of this structure, you can initialize these member variables:

// Create an instance of the Date structure
Date date;
// Initialize the attributes of Date
date.day = 1;
date.month = 10;
date.year = 2019;