Pointer to an array in C

Pointer to an Array

• A pointer to an array is a pointer that points to the first element of an array.

• In C, an array name can be treated as a pointer to the first element of the array.

The syntax for declaring a pointer to an array is as follows:

data_type (*ptr)[size];

Here, ptr is a pointer to an array of size elements of data type data_type.

For example, consider the following declaration:

int (*ptr)[5];

Explanation

• This declares ptr as a pointer to an array of 5 integers.
• You can use pointer to an array to access the elements of an array or to pass an array to a function.
• When you use a pointer to an array, you dereference it to access the elements of the array.

For example, consider the following code:

int arr[5] = {10, 20, 30, 40, 50};
int (*ptr)[5] = &arr;
printf("%d\n", (*ptr)[2]);

Here, ptr points to the first element of the arr array, and we dereference it to access the third element of the array, which is 30.

Pointer to an Array - Example 1

Example of using a pointer to an 1D array:

#include <stdio.h>

int main(void)
{
    int arr[5] = {10, 20, 30, 40, 50};
    int(*ptr)[5] = &arr; // ptr is a pointer to an array of 5 integers

    // Accessing elements of the array using the pointer
    printf("The third element is: %d\n", (*ptr)[2]);

    return 0;
}

Output:

Explanation

• ptr is a pointer to an array of 5 integers.
• The assignment ptr = &arr makes ptr point to the first element of the arr array.
• The statement (*ptr)[2] dereferences the pointer ptr and accesses the third element of the array.

Pointer to an Array - Example 2

Example of using a pointer to an 2D array:

#include <stdio.h>

void printArray(int (*ptr)[3], int rows)
{
    int i, j;
    for (i = 0; i < rows; i++)
    {
        for (j = 0; j < 3; j++)
        {
            printf("%d ", ptr[i][j]);
        }
        printf("\n");
    }
}

int main(void)
{
    int arr[2][3] = {{1, 2, 3}, {4, 5, 6}};
    int(*ptr)[3] = arr;

    printf("The 2D array elements are:\n");
    printArray(ptr, 2);

    return 0;
}

Output:

Explanation

• ptr is a pointer to an array of 3 integers, and arr is a 2D array of size "2 x 3".
• The assignment ptr = arr makes ptr point to the first element of the arr array.
• The function printArray takes a pointer to an array of 3 integers and the number of rows as arguments.
• Inside the function, a nested loop is used to print the elements of the 2D array.

array name

In C, an array name can be treated as a pointer to the first element of the array.