C++ Structures

C++ Structures

Structures (also called structs) are a way to group several related variables into one place.

Each variable in the structure is known as a member of the structure.

Unlike an array, a structure can contain many different data types: int, string, bool, etc.

Create a Structure

To create a structure, use the struct keyword and declare each of its members inside curly braces.

After the declaration, specify the name of the structure variable (myStructure in the example below):

struct {             // Structure declaration
  int myNum;         // Member (int
variable)
  string myString;   // Member (string variable)
}
myStructure;       // Structure variable

Access Structure Members

To access members of a structure, use the dot syntax (.):

Example

// Create a structure variable called myStructure
struct {
  int myNum;
  string myString;
} myStructure;

// Assign values to members of myStructure
myStructure.myNum = 1;
myStructure.myString = "Hello World!";

// Print members of myStructure
cout << myStructure.myNum << "\n";
cout << myStructure.myString << "\n";

One Structure in Multiple Variables

You can use a comma (,) to use one structure in many variables:

struct {
  int myNum;
  string myString;
} myStruct1, myStruct2, myStruct3; // Multiple structure variables separated with commas

This example shows how to use a structure in two different variables:

Example

struct {
  string brand;
  string model;
  int year;
} myCar1, myCar2;  // We can add variables by separating them with a comma here

// Put data into the first structure
myCar1.brand = "BMW";
myCar1.model = "X5";
myCar1.year = 1999;

// Put data into the second structure
myCar2.brand = "Ford";
myCar2.model = "Mustang";
myCar2.year = 1969;

// Print the structure members
cout << myCar1.brand << " " << myCar1.model << " " << myCar1.year << "\n";
cout << myCar2.brand << " " << myCar2.model << " " << myCar2.year << "\n";

Named Structures

By giving a name to the structure, you can treat it as a data type. This means that you can create variables with this structure anywhere in the program at any time.

To create a named structure, put the name of the structure right after the struct keyword:

struct car {  // This structure is now named "car"
  string
brand;
  string model;
  int year;
};

To declare a variable that uses the structure, use the name of the structure as the data type of the variable:

car myCar1;

Now the structure can be reused anywhere by using car as the data type:

Example

// Declare a structure named "car"
struct car {
  string brand;
  string model;
  int year;
};

int main() {
  // Create a car structure and store it in myCar1;
  car myCar1;
  myCar1.brand = "BMW";
  myCar1.model = "X5";
  myCar1.year = 1999;

  // Create another car structure and store it in myCar2;
  car myCar2;
  myCar2.brand = "Ford";
  myCar2.model = "Mustang";
  myCar2.year = 1969;

  // Print the structure members
  cout << myCar1.brand << " " << myCar1.model << " " << myCar1.year << "\n";
  cout << myCar2.brand << " " << myCar2.model << " " << myCar2.year << "\n";

  return 0;
}

Challenge Task

Create a structure to represent a student. It should have the following members:

• name (string)
• age (int)
• grade (char)

Then:

1. Create one variable of the structure.
2. Assign values to its members.
3. Print the values to the screen.

Expected Output

Name: Liam
Age: 35
Grade: A

Solution

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

struct student {
  string name;
  int age;
  char grade;
};

int main() {
  student s1;

  s1.name = "John";
  s1.age = 35;
  s1.grade = 'A';

  cout << "Name: " << s1.name << "\n";
  cout << "Age: " << s1.age << "\n";
  cout << "Grade: " << s1.grade << "\n";

  return 0;
}