In C, the name of an array is a constant pointer to the first element of the array. This means that arr (an array) and &arr[0] (the address of the first element) are equivalent.

Example

#include <stdio.h>

int main() {
    int arr[5] = {1, 2, 3, 4, 5}; // Declare and initialize an array

    // Print array elements using array indexing
    for (int i = 0; i < 5; i++) {
        printf("arr[%d] = %d\n", i, arr[i]);
    }

    // Print array elements using pointers
    for (int i = 0; i < 5; i++) {
        printf("*(arr + %d) = %d\n", i, *(arr + i));
    }

    return 0;
}

here, arr[i]: Accesses the ith element of the array, *(arr + i): Uses the array name (arr) as a pointer and adds i to get the address of the ith element. Dereferencing (*) this address gives the value of the ith element.

Pointer to an Array

You can also declare a pointer to an array and use it to access array elements.

Example

#include <stdio.h>

int main() {
    int arr[5] = {1, 2, 3, 4, 5}; // Declare and initialize an array
    int *ptr = arr; // Pointer to the first element of the array

    // Print array elements using the pointer
    for (int i = 0; i < 5; i++) {
        printf("*(ptr + %d) = %d\n", i, *(ptr + i));
    }

    return 0;
}

Array as Function Arguments

When passing an array to a function, what is actually passed is a pointer to the first element of the array.

Example

#include <stdio.h>

// Function to print array elements
void printArray(int *arr, int size) {
    for (int i = 0; i < size; i++) {
        printf("arr[%d] = %d\n", i, arr[i]);
    }
}

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

    printArray(arr, size); // Pass the array to the function

    return 0;
}

Multidimensional Arrays

A multidimensional array is an array of arrays. The most common form is a two-dimensional array, which can be thought of as a matrix or a table with rows and columns.

Example of a Two-Dimensional Array

#include <stdio.h>

int main() {
    int matrix[3][4] = {
        {1, 2, 3, 4},
        {5, 6, 7, 8},
        {9, 10, 11, 12}
    };

    // Accessing elements
    printf("Element at [1][2]: %d\n", matrix[1][2]); // Outputs 7

    return 0;
}

Pointers and Multidimensional Arrays

Array of Arrays

In the case of a two-dimensional array, each element of the main array is a sub-array. The name of the array acts as a pointer to the first sub-array.

int matrix[3][4]; // A two-dimensional array with 3 rows and 4 columns

Here, matrix can be considered as a pointer to an array of 4 integers.

Pointer to an Array

You can declare a pointer to an array and use it to access elements in a multidimensional array.

int (*ptr)[4]; // Pointer to an array of 4 integers
ptr = matrix;  // Points to the first row of the matrix

Accessing Elements Using Pointers

You can access elements of a multidimensional array using pointers with pointer arithmetic.

Example

#include <stdio.h>

int main() {
    int matrix[3][4] = {
        {1, 2, 3, 4},
        {5, 6, 7, 8},
        {9, 10, 11, 12}
    };

    int (*ptr)[4] = matrix; // Pointer to an array of 4 integers

    // Accessing elements using pointer arithmetic
    printf("Element at [1][2]: %d\n", *(*(ptr + 1) + 2)); // Outputs 7

    // Accessing elements using array notation with pointers
    printf("Element at [2][3]: %d\n", ptr[2][3]); // Outputs 12

    return 0;
}

Understanding how pointers interact with multidimensional arrays allows for efficient data manipulation and is fundamental for advanced programming in C.