Pointers & Structures

Expert Answer & Key Takeaways

Deep dive into advanced C concepts: Memory addresses, Pointers (declaration, initialization, arithmetic), and User-Defined Data Types (Structures and Unions).

Pointers & Structures in C

Pointers and Structures are advanced features that give C its incredible power and flexibility, allowing for direct memory manipulation and the creation of complex data types.

1. Pointers

A Pointer is a special variable that stores the memory address of another variable, rather than storing a standard data value like an integer or character.

1.1 Why use Pointers?

Dynamic Memory Allocation: Used with malloc() and free() to allocate memory during runtime.
Call by Reference: Passing pointers to functions allows the function to modify the original variable.
Array Manipulation: Pointers make iterating through arrays much faster and more efficient.

1.2 Declaring and Initializing a Pointer

To declare a pointer, use the asterisk * symbol. To get the address of a variable, use the 'address-of' & operator.

int age = 25;       // A normal integer variable
int *ptr = &age;    // 'ptr' is a pointer that stores the address of 'age'

1.3 Dereferencing a Pointer

To access or change the actual value stored at the memory address the pointer is holding, we use the * operator again. This is called Dereferencing.

printf("Address of age: %p", ptr); // Prints something like 0x7ffe...
printf("Value of age: %d", *ptr);  // Prints 25
*ptr = 30; // Changes the original 'age' variable to 30

1.4 Pointer Types

Null Pointer: A pointer that points to nothing (int *p = NULL;). Used to prevent accidental memory corruption.
Wild Pointer: An uninitialized pointer. It points to a random memory location and is highly dangerous.
Dangling Pointer: A pointer that points to a memory location that has already been deleted or freed.
Void Pointer: A generic pointer that can point to any data type (void *ptr;).

2. Structures (struct)

Arrays can only hold data of the same type. A Structure is a user-defined data type that groups together variables of different data types under a single name.

2.1 Defining and Declaring a Structure

// 1. Defining the structure template
struct Student {
    int rollNo;
    char name[50];
    float marks;
};

int main() {
    // 2. Creating a structure variable
    struct Student s1;
    
    // 3. Accessing members using the dot (.) operator
    s1.rollNo = 101;
    s1.marks = 89.5;
    
    return 0;
}

2.2 Array of Structures

Just like an array of integers, you can create an array of structures to store records for multiple entities (e.g., a database of 100 students). struct Student class10[100];

2.3 Pointers to Structures

If you have a pointer pointing to a structure, you cannot use the dot . operator to access its members. You MUST use the Arrow Operator (->).

struct Student s1;
struct Student *ptr = &s1;
ptr->rollNo = 101; // Using arrow operator

3. Unions

A Union is similar to a structure (it groups different data types), but with one major difference: Memory Sharing.

In a struct, every member gets its own separate memory space. Total size = sum of all members.
In a union, all members share the exact same memory location. Total size = size of the largest member.
Because they share memory, altering one member of a union will overwrite the data of the other members. You can only use one member at a time.

union Data {
    int i;
    float f;
    char str[20];
}; // Size of this union is 20 bytes (size of the largest member, the char array)

4. `typedef`

The typedef keyword is used to give a new, shorter nickname to an existing data type.

typedef unsigned long int ULI;
ULI distance = 500000; // Much easier to write than 'unsigned long int'

Course4All Editorial Board

Verified Expert

Subject Matter Experts

Comprising experienced educators and curriculum specialists dedicated to providing accurate, exam-aligned preparation material.

Pattern: 2026 Ready

Updated: Weekly

← Previous TopicFunctions & Arrays

Found an issue or have a suggestion?

Help us improve! Report bugs or suggest new features on our Telegram group.

Pointers & Structures

Expert Answer & Key Takeaways