How to Use Pointer to Array in C: Syntax and Examples

In C, a pointer to an array is declared by specifying the pointer to the entire array type, for example, int (*ptr)[5] points to an array of 5 integers. You use it to access or modify the whole array via the pointer by dereferencing it, like (*ptr)[index].

Syntax

To declare a pointer to an array, you specify the pointer with parentheses around the pointer name and the array size after it. For example:

• int (*ptr)[5]; declares ptr as a pointer to an array of 5 integers.
• (*ptr)[index] accesses the element at index in the array pointed to by ptr.

c

int (*ptr)[5];

Example

This example shows how to declare a pointer to an array, assign it to an existing array, and access elements through the pointer.

c

#include <stdio.h>

int main() {
    int arr[5] = {10, 20, 30, 40, 50};
    int (*ptr)[5] = &arr;  // Pointer to the whole array

    // Access elements using the pointer
    for (int i = 0; i < 5; i++) {
        printf("Element %d: %d\n", i, (*ptr)[i]);
    }

    // Modify an element through the pointer
    (*ptr)[2] = 100;
    printf("Modified element 2: %d\n", arr[2]);

    return 0;
}

Output

Element 0: 10
Element 1: 20
Element 2: 30
Element 3: 40
Element 4: 50
Modified element 2: 100

Common Pitfalls

Common mistakes when using pointers to arrays include:

• Confusing int *ptr (pointer to int) with int (*ptr)[5] (pointer to array of 5 ints).
• Not using parentheses correctly, which changes the meaning of the declaration.
• Trying to assign the pointer to just the first element instead of the whole array address.

Example of wrong and right declaration:

c

/* Wrong: ptr is pointer to int, not pointer to array */
int *ptr;
int arr[5];
ptr = arr; // points to first element, not whole array

/* Right: ptr is pointer to array of 5 ints */
int (*ptr)[5];
ptr = &arr; // points to whole array

Quick Reference

Concept	Syntax	Description
Pointer to array	int (*ptr)[N];	Pointer to an array of N elements of type int
Assign pointer	ptr = &array;	Assign address of whole array to pointer
Access element	(*ptr)[index]	Access element at index in the array pointed to
Difference	int *ptr vs int (*ptr)[N]	Pointer to element vs pointer to whole array

Key Takeaways

Use parentheses to declare a pointer to an array: int (*ptr)[size];

Assign the pointer to the address of the array: ptr = &array;

Access elements by dereferencing the pointer first: (*ptr)[index];

Do not confuse pointer to array with pointer to element.

Pointers to arrays allow passing or manipulating whole arrays efficiently.