A C structure tutorial

In C programming, a structure (or struct) is a user-defined data type that allows grouping of different data types together.

Structures help organize complex data by grouping variables (called members) under a single name, allowing for more readable and maintainable code, especially when dealing with related information.

1. Defining a Structure

To define a structure, use the struct keyword followed by the structure name and a set of braces containing the members of the structure.

struct StructureName {
    data_type member1;
    data_type member2;
    // Add more members as needed
};

• StructureName: The name of the structure.
• data_type: Data type of each member within the structure.
• member: The individual variable within the structure.

2. Basic Example of Structure Definition

Here’s a simple structure called Person, which groups information about a person’s name, age, and height.

#include <stdio.h>

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

int main() {
    struct Person person1;

    // Assign values to person1 members
    person1.age = 25;
    person1.height = 5.9;
    snprintf(person1.name, sizeof(person1.name), "John Doe");

    // Print person1 data
    printf("Name: %s\n", person1.name);
    printf("Age: %d\n", person1.age);
    printf("Height: %.1f\n", person1.height);

    return 0;
}

Explanation:

• struct Person defines a structure with three members: name, age, and height.
• person1 is a variable of type struct Person.
• Members are accessed using the dot (.) operator.

Output:

Name: John Doe
Age: 25
Height: 5.9

3. Initializing Structure Variables

Structures can be initialized when they are declared.

#include <stdio.h>

struct Book {
    char title[100];
    char author[50];
    int year;
};

int main() {
    struct Book book1 = {"The Great Gatsby", "F. Scott Fitzgerald", 1925};

    printf("Title: %s\n", book1.title);
    printf("Author: %s\n", book1.author);
    printf("Year: %d\n", book1.year);

    return 0;
}

Explanation:

• struct Book book1 = {…} initializes the structure members in the order they are defined.
• book1 is initialized directly at declaration.

Output:

Title: The Great Gatsby
Author: F. Scott Fitzgerald
Year: 1925

4. Accessing Structure Members

Structure members can be accessed using the dot (.) operator for individual structure variables.

#include <stdio.h>

struct Rectangle {
    int length;
    int width;
};

int main() {
    struct Rectangle rect = {10, 5};

    printf("Length: %d\n", rect.length);
    printf("Width: %d\n", rect.width);
    printf("Area: %d\n", rect.length * rect.width);

    return 0;
}

Explanation:

• rect.length and rect.width access the length and width members of rect.
• The area is calculated by multiplying the two members.

Output:

Length: 10
Width: 5
Area: 50

5. Array of Structures

You can create an array of structures to store multiple instances of the same structure type.

#include <stdio.h>

struct Student {
    char name[50];
    int age;
    float grade;
};

int main() {
    struct Student students[3] = {
        {"Alice", 20, 3.9},
        {"Bob", 21, 3.6},
        {"Charlie", 22, 3.8}
    };

    for (int i = 0; i < 3; i++) {
        printf("Name: %s, Age: %d, Grade: %.1f\n", students[i].name, students[i].age, students[i].grade);
    }

    return 0;
}

Explanation:

• struct Student students[3] defines an array of Student structures.
• The loop iterates over the array, printing each student’s details.

Output:

Name: Alice, Age: 20, Grade: 3.9
Name: Bob, Age: 21, Grade: 3.6
Name: Charlie, Age: 22, Grade: 3.8

6. Structure Pointers

You can use pointers to structures to dynamically allocate memory or pass structures to functions by reference.

#include <stdio.h>

struct Point {
    int x;
    int y;
};

int main() {
    struct Point p = {10, 20};
    struct Point *ptr = &p;

    printf("x = %d, y = %d\n", ptr->x, ptr->y);

    return 0;
}

Explanation:

• ptr is a pointer to p.
• ptr->x and ptr->y use the arrow operator (->) to access members of the structure through the pointer.

Output:

x = 10, y = 20

7. Passing Structures to Functions

Structures can be passed to functions by value or by reference.

Passing by Value

#include <stdio.h>

struct Circle {
    float radius;
};

void printArea(struct Circle c) {
    float area = 3.14159 * c.radius * c.radius;
    printf("Area: %.2f\n", area);
}

int main() {
    struct Circle c = {5.0};
    printArea(c);

    return 0;
}

Explanation:

• printArea receives a Circle structure by value, meaning it operates on a copy of the structure.

Output:

Area: 78.54

Passing by Reference

Passing by reference (using pointers) allows the function to modify the original structure.

#include <stdio.h>

struct Circle {
    float radius;
};

void doubleRadius(struct Circle *c) {
    c->radius *= 2; // Modifies the original radius
}

int main() {
    struct Circle c = {5.0};
    doubleRadius(&c);
    printf("Doubled Radius: %.2f\n", c.radius);

    return 0;
}

Explanation:

• doubleRadius receives a pointer to a Circle structure, allowing it to modify the original radius.

Output:

Doubled Radius: 10.00

8. Structures Within Structures (Nested Structures)

Structures can contain other structures as members.

#include <stdio.h>

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

struct Employee {
    char name[50];
    struct Date birthDate;
};

int main() {
    struct Employee emp = {"Alice", {15, 5, 1990}};

    printf("Employee Name: %s\n", emp.name);
    printf("Birth Date: %02d/%02d/%d\n", emp.birthDate.day, emp.birthDate.month, emp.birthDate.year);

    return 0;
}

Explanation:

• Employee has a Date structure as a member.
• emp.birthDate.day, emp.birthDate.month, and emp.birthDate.year access the nested structure members.

Output:

Employee Name: Alice
Birth Date: 15/05/1990

9. Typedef with Structures

Using typedef with structures simplifies code by allowing the structure to be referred to by a custom type name.

#include <stdio.h>

typedef struct {
    char title[50];
    char author[50];
    int year;
} Book;

int main() {
    Book b = {"1984", "George Orwell", 1949};

    printf("Title: %s\n", b.title);
    printf("Author: %s\n", b.author);
    printf("Year: %d\n", b.year);

    return 0;
}

Explanation:

• typedef struct { … } Book; defines a custom type Book, so struct keyword isn’t needed when declaring variables.

Output:

Title: 1984
Author: George Orwell
Year: 1949

10. Summary Table of Structure Examples

Complete Example

This example demonstrates using structures to manage a simple student database.

#include <stdio.h>

typedef struct {
    char name[50];
    int age;
    float gpa;
} Student;

void printStudent(Student s) {
    printf("Name: %s\n", s.name);
    printf("Age: %d\n", s.age);
    printf("GPA: %.2f\n", s.gpa);
}

int main() {
    Student students[3] = {
        {"Alice", 20, 3.9},
        {"Bob", 22, 3.7},
        {"Charlie", 19, 3.8}
    };

    for (int i = 0; i < 3; i++) {
        printf("Student %d:\n", i + 1);
        printStudent(students[i]);
        printf("\n");
    }

    return 0;
}

Explanation:

• Student is a structure with name, age, and gpa.
• students is an array of Student structures.
• printStudent takes a Student and prints their information.

Output:

Student 1:
Name: Alice
Age: 20
GPA: 3.9

Student 2:
Name: Bob
Age: 22
GPA: 3.7

Student 3:
Name: Charlie
Age: 19
GPA: 3.8

Structures in C provide an organized way to group related data, making it easier to manage complex information.