Structures in C

A structure is a user-defined data type that groups related variables of different data types together.

struct Student
{
    int id;
    char name[50];
    float marks;
};

Here, Student contains an integer, a character array, and a floating-point value.

Structures are useful for representing records containing related information.

• Student records
• Employee records
• Product details
• Book information
• Customer information
• Bank account records

The general syntax for defining a structure is:

struct StructureName
{
    data_type member1;
    data_type member2;
    data_type member3;
};

The semicolon after the closing brace is required.

struct Student
{
    int id;
    char name[50];
    float marks;
};

This defines a structure type named struct Student. It does not by itself create a variable named student.

After defining a structure, we can declare variables using the structure type.

struct Student student1;

Here, student1 is a structure variable.

The dot operator . is used to access members of a structure variable.

student1.id = 101;
student1.marks = 85.5;

Here, id and marks are members of student1.

A structure variable can be initialized when it is declared.

struct Student student1 = {
    101,
    "Rahul",
    85.5
};

The values are assigned to the members in the order in which they are declared.

C also supports designated initializers, which allow members to be initialized by name.

struct Student student1 = {
    .id = 101,
    .name = "Rahul",
    .marks = 85.5
};

This can make initialization clearer.

#include <stdio.h>

struct Student
{
    int id;
    char name[50];
    float marks;
};

int main()
{
    struct Student student1 = {101, "Rahul", 85.5};

    printf("ID: %d\n", student1.id);
    printf("Name: %s\n", student1.name);
    printf("Marks: %.2f\n", student1.marks);

    return 0;
}

Structure members can be filled using scanf() and other input functions.

struct Student student1;

printf("Enter ID: ");
scanf("%d", &student1.id);

printf("Enter marks: ");
scanf("%f", &student1.marks);

A character array inside a structure can be read using fgets().

printf("Enter name: ");
fgets(student1.name, sizeof(student1.name), stdin);

When using fgets(), remember that it may store the newline if the input fits in the buffer.

A structure can contain many different data types.

struct Employee
{
    int id;
    char name[50];
    float salary;
    char grade;
};

This allows related employee information to be stored together.

Multiple variables of the same structure type can be declared.

struct Student student1;
struct Student student2;
struct Student student3;

Each variable has its own copy of the structure members.

Two structure variables of the same structure type can be assigned to each other.

struct Student student1 = {101, "Rahul", 85.5};
struct Student student2;

student2 = student1;

The members of student1 are copied to student2.

An array can contain multiple structure variables.

struct Student students[3];

Each element of the array is a complete struct Student object.

students[0].id = 101;
students[1].id = 102;
students[2].id = 103;

for(int i = 0; i < 3; i++)
{
    printf("ID: %d\n", students[i].id);
    printf("Name: %s\n", students[i].name);
    printf("Marks: %.2f\n", students[i].marks);
}

A loop can process every structure in the array.

A structure can contain another structure as a member.

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

struct Student
{
    int id;
    char name[50];
    struct Date admissionDate;
};

Use multiple dot operators to access a nested structure member.

student1.admissionDate.day = 15;
student1.admissionDate.month = 8;
student1.admissionDate.year = 2026;

A pointer can store the address of a structure variable.

struct Student student1;

struct Student *ptr = &student1;

The pointer can be used to access the structure.

The arrow operator -> is used to access structure members through a pointer.

ptr->id = 101;
ptr->marks = 90.5;

The expression ptr->id is equivalent to (*ptr).id.

A structure can be passed to a function by value.

void display(struct Student s)
{
    printf("ID: %d\n", s.id);
    printf("Name: %s\n", s.name);
    printf("Marks: %.2f\n", s.marks);
}

The function receives a copy of the structure.

A pointer to a structure can be passed to a function.

void display(struct Student *s)
{
    printf("ID: %d\n", s->id);
    printf("Name: %s\n", s->name);
    printf("Marks: %.2f\n", s->marks);
}

This avoids copying the whole structure and allows the function to modify the original structure when the pointer is not const.

void updateMarks(struct Student *s)
{
    s->marks = 95.0;
}

int main()
{
    struct Student student1 = {101, "Rahul", 85.0};

    updateMarks(&student1);

    printf("%.2f", student1.marks);

    return 0;
}

The typedef keyword can create a shorter name for a structure type.

typedef struct
{
    int id;
    char name[50];
    float marks;
} Student;

Now we can declare:

Student student1;

instead of writing struct Student.

A function can receive a pointer to a constant structure when it only needs to read the structure.

void display(const struct Student *s)
{
    printf("%d\n", s->id);
    printf("%s\n", s->name);
    printf("%.2f\n", s->marks);
}

The function cannot modify the structure through s.

A structure definition must end with a semicolon.

struct Student
{
    int id;
    char name[50];
};

Forgetting the final semicolon causes a compilation error.

Use the dot operator with a structure variable and the arrow operator with a pointer to a structure.

struct Student student1;
struct Student *ptr = &student1;

student1.id = 101;
ptr->id = 102;

Using the wrong operator can result in a compilation error.

#include <stdio.h>

struct Student
{
    int id;
    char name[50];
    float marks;
};

void display(struct Student *s)
{
    printf("\nStudent Details\n");
    printf("ID: %d\n", s->id);
    printf("Name: %s\n", s->name);
    printf("Marks: %.2f\n", s->marks);
}

int main()
{
    struct Student student1;

    printf("Enter ID: ");
    scanf("%d", &student1.id);

    printf("Enter name: ");
    scanf("%49s", student1.name);

    printf("Enter marks: ");
    scanf("%f", &student1.marks);

    display(&student1);

    return 0;
}

This program creates a structure, takes input, and passes the structure to a function using a pointer.

Structures are widely used for organizing related information.

• Student management systems
• Employee management systems
• Library management systems
• Banking applications
• Product management
• Customer records
• Book records
• Inventory systems
• Data structures such as linked lists

Create a C program that:

1. Defines an Employee structure.
2. Stores employee ID, name, department, and salary.
3. Takes input from the user.
4. Displays the employee information.
5. Creates an array of 5 employees.
6. Displays all employees using a loop.
7. Uses a pointer to access an employee structure.
8. Creates a function to display employee details.

Try using both the dot operator . and arrow operator ->.