Pointers and Arrays in C programming

Pointers and Arrays in C programming

Pointers and Arrays in C programming

1. What is a Pointer?

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

Syntax:

data_type *pointer_name;

Example:

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

Here, ptr is a pointer to an integer variable x, storing its memory address.

2. What is an Array?

An array is a collection of elements of the same data type, stored in contiguous memory locations.

Example:

int arr[5] = {10, 20, 30, 40, 50};

Here, arr is an integer array of size 5.

3. Relationship Between Pointers and Arrays

  • The array name acts as a constant pointer to its first element.
  • The expression arr gives the memory address of arr[0].

Example:

#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30, 40, 50};
    int *ptr = arr;  // Pointer to array

    printf("First element: %d\n", *ptr);      // 10
    printf("Second element: %d\n", *(ptr+1)); // 20
    printf("Third element: %d\n", *(ptr+2));  // 30

    return 0;
}

Explanation:

  • ptr stores the address of arr[0]
  • *(ptr + 1) fetches the second element arr[1]
  • *(ptr + 2) fetches the third element arr[2]

4. Pointer Arithmetic with Arrays

Pointers support arithmetic operations like:

  • Increment (ptr++) → Moves to the next array element.
  • Decrement (ptr--) → Moves to the previous array element.
  • Addition (ptr + n) → Moves n elements ahead.
  • Subtraction (ptr - n) → Moves n elements back.

Example:

#include <stdio.h>

int main() {
    int arr[] = {5, 10, 15, 20, 25};
    int *ptr = arr;  // Points to arr[0]

    for(int i = 0; i < 5; i++) {
        printf("Element %d: %d\n", i, *(ptr + i));
    }

    return 0;
}

Output:

yamlCopyEditElement 0: 5
Element 1: 10
Element 2: 15
Element 3: 20
Element 4: 25

5. Arrays as Function Arguments

Since arrays are passed by reference, we can use pointers to manipulate arrays inside functions.

Example:

#include <stdio.h>

void modifyArray(int *arr, int size) {
    for(int i = 0; i < size; i++) {
        arr[i] *= 2;  // Doubling each element
    }
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int size = sizeof(arr) / sizeof(arr[0]);

    modifyArray(arr, size);

    for(int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }

    return 0;
}

Output:

2 4 6 8 10

Since we passed a pointer to the array, modifications inside modifyArray() reflect in main().

6. Dynamic Memory Allocation with Pointers

Using malloc, we can dynamically allocate memory for an array.

Example:

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *arr;
    int n = 5;

    // Allocating memory for 5 integers
    arr = (int*)malloc(n * sizeof(int));

    // Assigning values
    for(int i = 0; i < n; i++) {
        arr[i] = i + 1;
    }

    // Printing values
    for(int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }

    // Free allocated memory
    free(arr);

    return 0;
}

Output:

1 2 3 4 5

Here, we dynamically allocate memory for an array using malloc and free it using free().

Conclusion

Pointers and arrays are fundamental concepts in C programming that are deeply interconnected. Understanding their relationship allows for efficient memory management and optimized code execution.

Pointers and Arrays in C programming