What is a Structure?

A structure in C is like a container that can hold different types of data together. Think of it as a custom data type that groups related information under one name. It's similar to a form where you fill in different fields - each field can be a different data type!

For example, if you want to store information about a student, you might need:

• Name (string)
• Age (integer)
• Grade (float)

Instead of creating separate variables for each piece of information, you can group them together using a structure.

Defining a Structure

To create a structure, you use the struct keyword followed by a name and the member variables inside curly braces:

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

This creates a blueprint for a Student structure. Think of it as creating a template - you haven't created an actual student yet, just defined what a student should contain.

Declaring Structure Variables

Once you've defined a structure, you can create variables of that structure type:

struct Student student1;
struct Student student2;

You can also declare variables while defining the structure:

struct Student {
    char name[50];
    int age;
    float grade;
} student1, student2;

Accessing Structure Members

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

#include <stdio.h>
#include <string.h>

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

int main() {
    struct Student student1;
    
    // Assigning values
    strcpy(student1.name, "Alice");
    student1.age = 20;
    student1.grade = 85.5;
    
    // Accessing and printing values
    printf("Name: %s\n", student1.name);
    printf("Age: %d\n", student1.age);
    printf("Grade: %.1f\n", student1.grade);
    
    return 0;
}

Initializing Structures

You can initialize a structure when you declare it:

struct Student student1 = {"Bob", 19, 92.3};

Or you can use designated initializers (C99 and later):

struct Student student1 = {
    .name = "Charlie",
    .age = 21,
    .grade = 88.7
};

Complete Example

Here's a complete example that demonstrates structure basics:

#include <stdio.h>
#include <string.h>

struct Book {
    char title[100];
    char author[50];
    int pages;
    float price;
};

int main() {
    // Declare and initialize a structure variable
    struct Book book1 = {
        .title = "The C Programming Language",
        .author = "Dennis Ritchie",
        .pages = 272,
        .price = 29.99
    };
    
    // Declare another structure variable
    struct Book book2;
    
    // Assign values to book2
    strcpy(book2.title, "Learn C the Hard Way");
    strcpy(book2.author, "Zed Shaw");
    book2.pages = 298;
    book2.price = 34.95;
    
    // Display information
    printf("Book 1:\n");
    printf("Title: %s\n", book1.title);
    printf("Author: %s\n", book1.author);
    printf("Pages: %d\n", book1.pages);
    printf("Price: $%.2f\n\n", book1.price);
    
    printf("Book 2:\n");
    printf("Title: %s\n", book2.title);
    printf("Author: %s\n", book2.author);
    printf("Pages: %d\n", book2.pages);
    printf("Price: $%.2f\n", book2.price);
    
    return 0;
}

Key Points to Remember

• Structures group related data of different types
• Use struct keyword to define a structure
• Use the dot operator (.) to access structure members
• Structure members can be of any data type
• You can initialize structures during declaration or assign values later
• Structures help organize code and make it more readable

Structures are fundamental building blocks in C programming and are especially useful when dealing with complex data that has multiple attributes!