C structures are user-defined data types that allow programmers to group related variables of different data types under a single name. They provide a way to organize and manage complex data efficiently.

Defining a Structure

To define a structure in C, use the struct keyword followed by the structure name and a block containing member variables:

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

Declaring Structure Variables

Once defined, you can declare variables of the structure type:

struct Person person1, person2;

Alternatively, you can combine the definition and declaration:

struct Person {
    char name[50];
    int age;
    float height;
} person1, person2;

Accessing Structure Members

Use the dot (.) operator to access individual members of a structure:

strcpy(person1.name, "John Doe");
person1.age = 30;
person1.height = 1.75;

Initializing Structures

You can initialize a structure at declaration time:

struct Person person3 = {"Jane Smith", 25, 1.68};

Structures and Functions

Structures can be passed to functions as arguments or returned from functions. This allows for modular and organized code:

void printPerson(struct Person p) {
    printf("Name: %s\nAge: %d\nHeight: %.2f\n", p.name, p.age, p.height);
}

// Usage
printPerson(person1);

Nested Structures

Structures can contain other structures as members, allowing for more complex data organization. For more information on this topic, see C Nested Structures.

Pointers to Structures

You can create pointers to structures, which is useful for dynamic memory allocation and efficient function parameter passing:

struct Person *personPtr = &person1;
printf("Name: %s\n", personPtr->name);  // Use -> operator with pointers

Important Considerations

Structures are passed by value to functions by default, which can be inefficient for large structures. Consider using pointers or references instead.
Memory alignment may cause padding between structure members, affecting the total size of the structure.
When using structures with dynamic memory allocation, remember to free all allocated memory to prevent memory leaks.

Applications of Structures

Structures are widely used in C programming for various purposes:

Representing complex data types (e.g., date, time, geometric shapes)
Implementing abstract data types like linked lists, trees, and graphs
Organizing related data in databases or file I/O operations
Creating custom data structures for specific application needs

By mastering C structures, you'll be able to write more organized and efficient code, especially when dealing with complex data relationships. For more advanced usage, consider exploring C Unions and C Typedef to further enhance your data structuring capabilities.