C (programming language)

C Program to Show How to Handle Pointers

Understanding Pointers in C

  • Pointers: Variables that store memory addresses, providing direct access to data stored at those addresses.
  • Key Concepts:
    • Declaration: Using the * operator to declare pointer variables.
    • Dereferencing: Accessing the value at a memory address using the * operator.
    • Address-of operator: & to get the memory address of a variable.
    • Pointer arithmetic: Performing operations on pointers to navigate memory.

Step-by-Step Guide

1. Header Inclusion


#include <stdio.h>
  • Explanation: Includes the standard input/output library for functions like printf.

2. Main Function


int main() {
    // Code statements here
    return 0;

3. Pointer Declaration


int num = 10;  // Regular integer variable
int *ptr;      // Pointer variable to hold an integer address
  • Explanation:
    • num: Declares an integer variable with value 10.
    • ptr: Declares a pointer variable that can hold the address of an integer.

4. Assigning Address to Pointer


ptr = &num;  // Assigning the address of num to ptr
  • Explanation: The & operator gets the memory address of num and assigns it to ptr.

5. Accessing Value Through Pointer (Dereferencing)


printf("Value of num: %d\n", *ptr);  // Accessing the value at the address pointed to by ptr
  • Explanation: The * operator dereferences ptr, accessing the value stored at the memory address it points to.

6. Modifying Value Through Pointer


*ptr = 20;  // Modifying the value at the address pointed to by ptr
printf("New value of num: %d\n", num);  // Changes will reflect in the original variable
  • Explanation: Modifying the value using *ptr directly changes the value of num in memory.

7. Pointer Arithmetic


int arr[] = {1, 2, 3, 4, 5};  // Array declaration
int *arrPtr = arr;           // Pointer pointing to the first element of the array

printf("Second element: %d\n", *(arrPtr + 1));  // Accessing elements using pointer arithmetic
printf("Address of third element: %p\n", arrPtr + 2);  // Adding offsets to pointers
  • Explanation: Pointer arithmetic allows navigating through arrays using pointers.

8. Complete Code Example


#include <stdio.h>

int main() {
    int num = 10;
    int *ptr = &num;

    printf("Value of num: %d\n", *ptr);

    *ptr = 20;
    printf("New value of num: %d\n", num);

    int arr[] = {1, 2, 3, 4, 5};
    int *arrPtr = arr;

    printf("Second element: %d\n", *(arrPtr + 1));
    printf("Address of third element: %p\n", arrPtr + 2);

    return 0;

9. Essential Pointer Concepts

  • Null Pointers: Pointers that don’t point to any valid memory address, often used to indicate the end of data structures or errors.
  • Pointers and Functions: Passing pointers to functions allows functions to modify variables in the calling scope.
  • Dynamic Memory Allocation: Using pointers to allocate and deallocate memory dynamically during program execution (e.g., with malloc and free).

Remember that pointers are powerful but can also lead to errors if not used carefully. Practice and understanding are key to mastering pointer manipulation in C.


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