Structure

Definition

• Structures are aggregate data types built using elements of other types.
• Structures are defined using the keyword struct, followed by the declarations of the elments within the structure.
• Syntax:

  struct <struct_name>
  {
    datatype1 identifier1
    datatype2 identifier2
    …..
    datatypen identifiern
    and so on
  }
  

Description

• Structure members can be of any type.
• One structure may contain members of many different type.
• When we define a structure is like we are defining a new data type of our design.
• We can then declare variables, arrays or pointers of the type of structure that we have defined.

Example

struct student
{
    int roll;
    char name[20];
    float marks;
};

struct car
{
    char name[20];
    int year;
    float price;
};

Now we can have variables of the structure we declare:

struct student s1;// a single object of type student
struct student s2, s3;// two objects of type student
struct student s4[10];// an array of 10 objects of type student

struct car *mercedes;// a pointer to a car object
struct car *bmw, *audi;// two pointers to car objects

Accessing Members of Structure

• Members of a structure are accessed using the member access operators – known as the dot operator . and the arrow operator -> ```C++ struct student { int roll; char name[20]; float marks; };

int main() { struct student s1; s1.roll = 1; strcpy(s1.name, “John”); s1.marks = 90.5; return 0; }

output:
```C++
1
John
90.5

• The expression timePtr->hour is the same as (*timePtr).hour ```C++ struct time { int hour; int minutes; int seconds; };

int main() { struct time t1; struct time *timePtr; timePtr = &t1; timePtr->hour = 10; timePtr->minutes = 20; timePtr->seconds = 30; return 0; }

output:
```C++
10
20
30

Structure Arrays

• We can declare arrays of structures.
• The syntax is similar to that of declaring arrays of other data types. ```C++ struct person { char name[20]; int age; float salary; };

int main() { struct person p1[3];

for (int i = 0; i < 3; i++)
{
    cout << "Enter name: ";
    cin >> p1[i].name;
    cout << "Enter age: ";
    cin >> p1[i].age;
    cout << "Enter salary: ";
    cin >> p1[i].salary;
}

cout << "Displaying Information:" << endl;
for (int i = 0; i < 3; i++)
{
    cout << "Name: " << p1[i].name << endl;
    cout << "Age: " << p1[i].age << endl;
    cout << "Salary: " << p1[i].salary << endl;
}

return 0; } ```

Pointers to Structures

• We can declare pointers to structures.
• The syntax is similar to that of declaring pointers to other data types. ```C++ struct person { char name[20]; int age; float salary; };

int main() { struct person p1; struct person *ptr; // or we can just write struct person *ptr = &p1; ptr = &p1; cout « “Enter name: “; cin » ptr->name; cout « “Enter age: “; cin » ptr->age; cout « “Enter salary: “; cin » ptr->salary; cout « “Displaying Information:” « endl; cout « “Name: “ « ptr->name « endl; cout « “Age: “ « ptr->age « endl; cout « “Salary: “ « ptr->salary « endl; return 0; }

## Nested Structures

- We can define structures within structures.
- The syntax is similar to that of defining structures.
```C++
struct address
{
    char city[20];
    char state[20];
    char country[20];
};

struct person
{
    char name[20];
    int age;
    float salary;
    struct address add; // or just address add;
};

int main()
{
    struct person p1;
    cout << "Enter name: ";
    cin >> p1.name;
    cout << "Enter age: ";
    cin >> p1.age;
    cout << "Enter salary: ";
    cin >> p1.salary;
    cout << "Enter city: ";
    cin >> p1.add.city;
    cout << "Enter state: ";
    cin >> p1.add.state;
    cout << "Enter country: ";
    cin >> p1.add.country;
    cout << "Displaying Information:" << endl;
    cout << "Name: " << p1.name << endl;
    cout << "Age: " << p1.age << endl;
    cout << "Salary: " << p1.salary << endl;
    cout << "City: " << p1.add.city << endl;
    cout << "State: " << p1.add.state << endl;
    cout << "Country: " << p1.add.country << endl;
    return 0;
}