18. C++ Structures

C++ Structures

In this article, you'll learn about structures in C++ programming; what is it, how to define it and use it in your program.

Structure is a collection of variables of different data types under a single name. It is similar to a class in that, both holds a collecion of data of different data types.
For example: You want to store some information about a person: his/her name, citizenship number and salary. You can easily create different variables name, citNo, salary to store these information separately.
However, in the future, you would want to store information about multiple persons. Now, you'd need to create different variables for each information per person: name1, citNo1, salary1, name2, citNo2, salary2
You can easily visualize how big and messy the code would look. Also, since no relation between the variables (information) would exist, it's going to be a daunting task.
A better approach will be to have a collection of all related information under a single name Person, and use it for every person. Now, the code looks much cleaner, readable and efficient as well.
This collection of all related information under a single name Person is a structure.

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How to declare a structure in C++ programming?

The struct keyword defines a structure type followed by an identifier (name of the structure).
Then inside the curly braces, you can declare one or more members (declare variables inside curly braces) of that structure. For example:

struct Person
{
    char name[50];
    int age;
    float salary;
};

Here a structure person is defined which has three members: name, age and salary.
When a structure is created, no memory is allocated.
The structure definition is only the blueprint for the creating of variables. You can imagine it as a datatype. When you define an integer as below:

int foo;

The int specifies that, variable foo can hold integer element only. Similarly, structure definition only specifies that, what property a structure variable holds when it is defined.
Note: Remember to end the declaration with a semicolon (;)

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How to define a structure variable?

Once you declare a structure person as above. You can define a structure variable as:

Person bill;

Here, a structure variable bill is defined which is of type structure Person.
When structure variable is defined, only then the required memory is allocated by the compiler.
Considering you have either 32-bit or 64-bit system, the memory of float is 4 bytes, memory of int is 4 bytes and memory of char is 1 byte.
Hence, 58 bytes of memory is allocated for structure variable bill.

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How to access members of a structure?

The members of structure variable is accessed using a dot (.) operator.
Suppose, you want to access age of structure variable bill and assign it 50 to it. You can perform this task by using following code below:

bill.age = 50;

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Example: C++ Structure

C++ Program to assign data to members of a structure variable and display it.

#include <iostream>
using namespace std;

struct Person
{
    char name[50];
    int age;
    float salary;
};

int main()
{
    Person p1;
    
    cout << "Enter Full name: ";
    cin.get(p1.name, 50);
    cout << "Enter age: ";
    cin >> p1.age;
    cout << "Enter salary: ";
    cin >> p1.salary;

    cout << "\nDisplaying Information." << endl;
    cout << "Name: " << p1.name << endl;
    cout <<"Age: " << p1.age << endl;
    cout << "Salary: " << p1.salary;

    return 0;
}

Output

Enter Full name: Magdalena Dankova
Enter age: 27
Enter salary: 1024.4

Displaying Information.
Name: Magdalena Dankova
Age: 27
Salary: 1024.4

Here a structure Person is declared which has three members name, age and salary.
Inside main() function, a structure variable p1 is defined. Then, the user is asked to enter information and data entered by user is displayed