Pointers

What is a pointer?

• A pointer is a variable that stores the address of another variable.
• It is used to store the memory address of a variable.

Why use pointers?

• To access the memory address of a variable.
• To access the value of a variable indirectly.
• To pass arguments by reference.
• To return multiple values from a function.
• To allocate memory dynamically.

Pointer Declaration

• The declaration of a pointer is similar to the declaration of a variable.
• The data type of a pointer must be the same as the data type of the variable it points to.
• The pointer declaration is done by adding an asterisk (*) before the pointer name.

int *ptr;

Pointer Initialization

• A pointer can be initialized with the address of a variable.
• The address of a variable can be obtained by using the address-of operator (&).

int num = 10;
int *ptr = #

Pointer Dereferencing

• Dereferencing a pointer means accessing the value of the variable it points to.
• The value of a variable can be accessed by using the dereference operator (*).

int num = 10;
int *ptr = #
printf("%d", *ptr); // Output: 10

Pointer Arithmetic

• Pointer arithmetic is used to perform arithmetic operations on pointers.
• The arithmetic operations include addition, subtraction, increment, and decrement.
• The size of the data type is taken into account when performing arithmetic operations.

int arr[5] = {1, 2, 3, 4, 5};
int *ptr = arr;
printf("%d", *ptr); // Output: 1
ptr++;
printf("%d", *ptr); // Output: 2

Pass-by-value

• In C, arguments are passed to functions by value.
• It means that a copy of the data is made and used inside the function, not affecting the original data.

void increment(int num){
  num++;
}
 
int num = 10;
increment(num);
printf("%d", num); // Output: 10

Pass-by-reference

• Pointers can be passed as arguments to functions.
• Passing a pointer as an argument allows the function to modify the value of the variable it points to.

void increment(int *ptr){
    (*ptr)++;
}
 
int num = 10;
increment(&num);
printf("%d", num); // Output: 11

Pointer to Array

• A pointer to an array is a pointer that stores the address of the first element of an array.
• It is used to access the elements of an array using pointer arithmetic.

int arr[5] = {1, 2, 3, 4, 5};
int *ptr = arr;
printf("%d", *ptr); // Output: 1
ptr++;
printf("%d", *ptr); // Output: 2

Pointer to Structure

• A pointer to a structure is a pointer that stores the address of a structure.
• It is used to access the members of a structure using the arrow operator (->).

struct Point{
    int x;
    int y;
};
 
struct Point p = {10, 20};
struct Point *ptr = &p;
printf("%d", ptr->x); // Output: 10
printf("%d", ptr->y); // Output: 20

Null Pointer

• A null pointer is a pointer that does not point to any memory location.
• It is used to indicate that the pointer is not pointing to a valid memory address.
• It is represented by the constant NULL.

int *ptr = NULL;
if(ptr == NULL){
    printf("Null Pointer");
}