In C language, a pointer is a variable that holds the memory address of another variable. Pointers are used to directly access and manipulate memory locations, which can be useful for a variety of tasks such as dynamic memory allocation, passing variables to functions by reference, and creating data structures such as linked lists and trees.

A pointer variable is declared by placing an asterisk (*) before the variable name, followed by the type of the variable it points to. For example, the following declares a pointer variable p that points to an integer variable:

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int* p;

The address operator (&) is used to obtain the memory address of a variable. For example, the following assigns the memory address of the variable x to the pointer variable p:

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int x = 10; int* p = &x;

The dereference operator (*) is used to access the value stored at a memory address. For example, the following assigns the value stored at the memory address held by p to the variable y:

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int y = *p;

Pointers can also be used to dynamically allocate memory using the malloc() or calloc() functions from the stdlib.h library. These functions return a pointer to a block of memory on the heap, which can be used to store variables of any type.

Here is an example of allocating memory dynamically to pointer variable:

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#include <stdio.h> #include <stdlib.h> int main() {    int* ptr = (int*)malloc(size