Structures In C++

Syntax Of Structure in C++

struct StructureName {
   dataType member1;
   dataType member2;
   // more members...
};

How to create a structure?

A structure is created using a keyword struct. Structures in C++ can contain:

• Data Members:- These are normal variables in C++
• Member Functions:- These are normal functions in C++

struct Employee {        
string name;        
int age;       
float salary; };

Note: Always end structure definition with a semicolon, as shown above.

Let’s move towards understanding member functions inside structures in C++, it is worth noting that structures defined in C cannot have member functions, however, structures in C++ allow having member functions along with data members.

struct Employee {     // Data Members     
string name;     
int age;     
float salary;     
// Member functions (Only in C++)     
void display(){         
cout << “The employee age is: ” << age;     
} };

Now to make use of this structure, we have to make structure variables, but before that, I want to share an important concept i.e.No memory is allocated when you create a structure. Now you must be wondering why it is so? Let me clarify this here, see structures in C++ are like the blueprint for variable creation. Space will be allocated only when you create structure variables.

How to make Structure Variables?

In C++ you can define structure Variables in two ways:-

• Define a structure variable in a separate declaration like you define primitive data type variables in C++.

struct Employee {        string name;        int age;       float salary; };

Note: In C++, writing struct keyword before the declaration of a variable is optional i.e., we can also write Employee e1;  instead of struct Employee e1;

• The second way is to define a structure variable is defining them at the time of structure declaration:

struct Employee {        string name;        int age;       float salary; }e1; //variable is declared with Employee

You can define as many structure variables as you want. Suppose you want to store information of 5 Employees, then you can make five structure variables. Now we’ve learned to define structure variables, so next, we should learn about accessing the data members inside structures using these structure variables.

How to declare structure variables?

To declare structure variables, you first define the structure using the struct keyword, then create variables of that structure type. You can declare multiple variables in a single line or one at a time.

Code Implementation:

• C++

C++

#include <iostream>
#include <string>

struct Book {
    std::string title;
    std::string author;
    int publicationYear;
    float price;
};

int main() {
    // Declaring structure variables
    Book book1;  // Declare a single variable
    Book book2;  // Declare another variable

    // Initializing book1
    book1.title = "1984";
    book1.author = "George Orwell";
    book1.publicationYear = 1949;
    book1.price = 15.99;

    // Initializing book2
    book2.title = "To Kill a Mockingbird";
    book2.author = "Harper Lee";
    book2.publicationYear = 1960;
    book2.price = 10.99;

    // Displaying book details
    std::cout << "Book 1:\n";
    std::cout << "Title: " << book1.title << "\n";
    std::cout << "Author: " << book1.author << "\n";
    std::cout << "Publication Year: " << book1.publicationYear << "\n";
    std::cout << "Price: $" << book1.price << "\n\n";

    std::cout << "Book 2:\n";
    std::cout << "Title: " << book2.title << "\n";
    std::cout << "Author: " << book2.author << "\n";
    std::cout << "Publication Year: " << book2.publicationYear << "\n";
    std::cout << "Price: $" << book2.price << "\n";

    return 0;
}

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Output:

Book 1:
Title: 1984
Author: George Orwell
Publication Year: 1949
Price: $15.99

Book 2:
Title: To Kill a Mockingbird
Author: Harper Lee
Publication Year: 1960
Price: $10.99

How to Access Members of a Structure?

The dot operator(.) is used in C++ to access structure members i.e the data members and member functions. Suppose you want to access the age of an employee, then you can write e1.age;  

You can also assign a value using a dot operator like e1.age = 30;    

We can initialize structure variables without using the dot operator also. Let’s see programs by both ways to initialize structure variables.

• C++

C++

// C++ program using dot operator
#include <iostream>
#include <string>
using namespace std;

// Creating a structure named Employee
struct Employee {
    string name;
    int age;
    float salary;

    void display() {
        cout << "Name: " << name << endl;
        cout << "Age: " << age << endl;
        cout << "Salary: " << salary << endl;
    }
};

int main() {
    // Making variable of the structure defined above
    Employee e1;

    // Accessing data member inside structure using structure variable
    cout << "Enter your name: ";
    cin >> e1.name;
    cout << "Enter your age: ";
    cin >> e1.age;
    cout << "Enter your salary: ";
    cin >> e1.salary;

    // Accessing member function inside structure using structure variable
    e1.display();

    return 0;
}

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C++ Program Without Using Dot Operator

• C++

C++

// C++ program without using dot operator
#include <iostream>
#include <string>
using namespace std;

struct Employee {
    string name;
    int age;
    float salary;

    void display() {
        cout << "Name: " << name << endl;
        cout << "Age: " << age << endl;
        cout << "Salary: " << salary << endl;
    }
};

int main() {
    // Order of structure variables will be followed in initialization
    Employee e1 = { "Ninja", 15, 500000 };
    e1.display();

    return 0;
}

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So, from the above two codes, you’ve mastered two ways of initializing variables in the structures in C++. One way is to initialize the variables using dot operator and the second way is without using dot operator but here, with the second method, you need to be careful with the order of values you are passing.

Values should be passed in the same order as you have defined variables in the structure otherwise you will get unexpected results. Now let’s discuss structure pointers.

Pointers To Structure in C++

In C++, you must have worked with pointer variables for primitive data types like int, float, and char in C++. We can also make pointers for user-defined data types like structures here. Before moving forward, if you want to know more about pointers, then have a look here.

Let’s see a program where we will make a pointer variable to a structure:

#include <iostream> 
using namespace std; 
struct Employee {        
string name;        
int age;       
float salary; }; 
int main(){        
Employee* e;       
return 0; }

In this program, we created a pointer e of user-defined data type Employee. To access data members with a pointer, you have to use the arrow operator (->) instead of dot operator(.)

Let’s modify the program discussed above using pointers so that it can become crystal clear to you.

• C++

C++

#include <iostream>
#include <string>
using namespace std;

// Defining the Employee structure
struct Employee {
    string name;
    int age;
    float salary;
};

int main() {
    // Dynamically allocating memory for an Employee object
    Employee* e1 = new Employee;

    // Getting input from the user
    cout << "Enter your name: ";
    cin >> e1->name;  // Using arrow operator to access members
    cout << "Enter your age: ";
    cin >> e1->age;
    cout << "Enter your salary: ";
    cin >> e1->salary;

    // Displaying the details of the employee
    cout << "Name: " << e1->name << endl;
    cout << "Age: " << e1->age << endl;
    cout << "Salary: " << e1->salary << endl;

    // Deallocating the dynamically allocated memory
    delete e1;

    return 0;
}

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So in this program, you first created a structure pointer and then used that to access structure members.

How to initialize structure members? 

Structure members can be initialized in several ways in C++. Here are three common methods: using a constructor, using an initialization list, and directly initializing during declaration.

Code Implementation:

• C++

C++

#include <iostream>
#include <string>
using namespace std;

// Defining the Employee structure
struct Employee {
    string name;
    int age;
    float salary;

    // Constructor to initialize members
    Employee(string n, int a, float s) : name(n), age(a), salary(s) {}
};

int main() {
    // Method 1: Using a constructor to initialize members
    Employee e1("Rahul", 30, 60000.50);
    
    // Method 2: Using an initialization list during declaration
    Employee e2 = { "Rohit", 25, 50000.00 };
    
    // Method 3: Direct assignment after declaration
    Employee e3; // Declare without initialization
    e3.name = "Mohit"; // Assigning values to members
    e3.age = 28;
    e3.salary = 55000.75;

    // Displaying the details of each employee
    cout << "Employee 1: " << e1.name << ", Age: " << e1.age << ", Salary: Rs." << e1.salary << endl;
    cout << "Employee 2: " << e2.name << ", Age: " << e2.age << ", Salary: Rs." << e2.salary << endl;
    cout << "Employee 3: " << e3.name << ", Age: " << e3.age << ", Salary: Rs." << e3.salary << endl;

    return 0;
}

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Output:

Employee 1: Rahul, Age: 30, Salary: Rs.60000.5
Employee 2: Rohit, Age: 25, Salary: Rs.50000
Employee 3: Mohit, Age: 28, Salary: Rs.55000.75

Frequently Asked Questions

Why do we need structures in C++?

We need structures to store variables of different data types in a single container. Unlike arrays in C++, Structures in C++ can store int value, float value, or whatever data type you want to keep.

How are structures in C++ different from classes in C++?

The significant difference between classes and structures in C++ is from a security perspective. By default, class members have private access specifiers, but structure members have public access specifiers by default. Another difference is that the class needs to have a constructor and a destructor, whereas there is no such need for structures in C++.

What is the benefit of struct in C++?

The benefit of using structures in C++ lies in their ability to group related data items of different types into a single unit, enhancing code organization, readability, and maintainability. They also facilitate better data modeling for complex entities.

Can I have an array of structures?

Yes! You can. The structure is just another user-defined data type and we can do the same things with structs as we do with primitive data types.

Conclusion

In this blog, we have discussed structures in C++. They are a powerful tool for organizing and managing related data. By allowing the grouping of different data types under a single name, structures enhance code clarity and facilitate better data modeling. They serve as a foundation for more complex data structures, making them essential in both simple and advanced programming tasks.