Pointers C

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The memory address of other variables, functions, or even other pointers can be stored in a pointer, which is a derived data type. It is one of the fundamental elements of the C programming language, enabling dynamic memory allocation, low-level memory access, and numerous other features.

Basic Concepts of Pointers:

Instead of a variable's actual value, a pointer contains the variable's address.
The value at the address included in the pointer can be accessed using the dereference operator *.
To find a variable's memory address, use the address-of operator &.

Example:
#include <stdio.h>

int main() {
    int var = 10;         // Normal variable
    int *ptr;             // Pointer to an integer

    ptr = &var;           // Storing the address of 'var' in 'ptr'

    printf("Value of var: %d\n", var);          // Prints value of var
    printf("Address of var: %p\n", &var);      // Prints address of var
    printf("Value of ptr: %p\n", ptr);         // Prints value of ptr (address of var)
    printf("Value pointed by ptr: %d\n", *ptr); // Dereferencing pointer to get the value of var

    return 0;
}

Pointer Declaration: A pointer is declared by specifying the type of data it points to, followed by an asterisk *.

int *ptr;  // Pointer to an integer

Pointer Initialization: You can initialize a pointer by assigning it the memory address of a variable using the address-of operator &

int x = 10;
int *ptr = &x;  // ptr now holds the address of x

Dereferencing a Pointer: Dereferencing a pointer means accessing the value stored at the memory address the pointer is pointing to. You use the * operator to dereference a pointer.

Example:
int x = 10;
int *ptr = &x;
printf("%d", *ptr);  // Output will be 10, as ptr points to x

Pointer to Pointer: You can have pointers to other pointers, which means that a pointer can store the address of another pointer.

Example:

int x = 10;

int *ptr = &x;

int **ptr2 = &ptr;  // ptr2 points to ptr, which points to x

printf("%d", **ptr2);  // Output will be 10

Null Pointer: A pointer that does not point to any legitimate memory location is known as a null pointer. It is frequently used to show that there is no data being pointed to by the pointer.
Example:
int *ptr = NULL;  // ptr is a null pointer

Pointer Arithmetic: Arithmetic operations are supported by pointers in C. A pointer can be increased, decreased, or even subtracted by two.

int arr[3] = {10, 20, 30};
int *ptr = arr;
printf("%d\n", *(ptr + 1));  // Output will be 20, points to second element

Dynamic Memory Allocation: For dynamic memory allocation and deallocation, pointers are utilized using functions such as malloc, calloc, and free.

int *ptr = (int*)malloc(sizeof(int));  // Dynamically allocate memory
*ptr = 5;  // Assign value
printf("%d\n", *ptr);  // Output will be 5
free(ptr);  // Deallocate memory

Example:

#include <stdio.h>

int main() {
    int a = 10;
    int *ptr = &a;  // Pointer to the integer a

    printf("Address of a: %p\n", ptr);  // Print address stored in ptr
    printf("Value of a: %d\n", *ptr);  // Dereference pointer to get value

    *ptr = 20;  // Modify value of a through the pointer
    printf("New value of a: %d\n", a);  // Output will be 20

    return 0;
}




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