FOC Unit IV: Pointer

 

What is a Pointer?
A pointer is a variable that stores the memory address of another variable.

• Normal variable → stores value
• Pointer variable → stores the address of a value.

Declaring a Pointer

Syntax:     data_type *pointer_name;

Example:     int *p; // p is a pointer to an integer

Assigning Address to a Pointer

Use & (address-of operator) to store the address of a variable.

Example

int a = 10;
int *p;

p = &a;   // p stores the address of a

Accessing Value Using Pointer
Use * (dereference operator) to get the value stored at the address held by the pointer.
Example
printf("%d", *p);  // prints value of a (10)

Pointer Example Program
#include <stdio.h>

int main() {
    int a = 10;
    int *p;       // pointer declaration
    p = &a;       // store address of a in pointer

    printf("Value of a: %d\n", a);
    printf("Address of a: %p\n", &a);
    printf("Pointer p stores: %p\n", p);
    printf("Value at pointer p: %d\n", *p);

    return 0;
}

Important Pointer Operators

Operator
Meaning
&
Address of a variable
*
Value at the address (dereference)
Why Use Pointers? 
To access and modify values directly from memory.
For dynamic memory allocation (malloc, calloc).
To pass large arrays or structures to functions efficiently.
Used in data structures (linked list, tree, etc.).

Pointer to Pointer (Basic Concept)
A pointer that stores the address of another pointer.
Example
int a = 5;
int *p = &a;
int **pp = &p;   // pointer to pointer

#Example:

#include <stdio.h>

int main() {
    int a = 5;        // normal integer variable
    int *p = &a;      // pointer to integer
    int **pp = &p;    // pointer to pointer

    printf("Value of a = %d\n", a);
    printf("Address of a = %p\n", &a);

    printf("\nValue stored in p (address of a) = %p\n", p);
    printf("Value pointed by p (*p) = %d\n", *p);

    printf("\nValue stored in pp (address of p) = %p\n", pp);
    printf("Value pointed by pp (*pp) = %p\n", *pp);
    printf("Value pointed by pointer to pointer (**pp) = %d\n", **pp);

    return 0;
}

#output Explanation
a stores 5
p stores address of a
pp stores address of p
*p gives value of a
*pp gives value of p (i.e., address of a)
**pp gives value of a through double dereferencing


Pointer and Array Relationship (Basic)
Array name itself acts like a pointer.
Example
int arr[3] = {10, 20, 30};
int *p = arr;

printf("%d", *p);     // prints 10
printf("%d", *(p+1)); // prints 20

Array of Pointers (Pointer Array)
Definition
An array of pointers is an array where each element is a pointer (not a normal variable).
It is useful to store:
addresses of variables
addresses of strings
dynamic data

Syntax
data_type *array_name[size];

Example: Array of Integer Pointers
int a = 10, b = 20, c = 30;

int *ptr[3];   // array of 3 integer pointers

ptr[0] = &a;
ptr[1] = &b;
ptr[2] = &c;

printf("%d", *ptr[1]);   // prints 20

Example: Array of Strings 
char *names[] = {"MITAOE", "Computer", "Engineering"};
printf("%s", names[0]);  // prints MITAOE
printf("%s", names[2]);  // prints Engineering