---
title: 6.10 Passing Arrays to Functions
description: When an array is passed to a function, its name is converted to a pointer to its first element. The function can access and modify the original array elements through that pointer. The array length is typically passed as a…
url: "https://edcret.in/docs/c-programming/c-functions/6-10-passing-arrays-to-functions/"
updated: "2026-10-27"
category: C Programming / Functions
---

# 6.10 Passing Arrays to Functions

When an array is passed to a function, its name is converted to a pointer to its first element. The function can access and modify the original array elements through that pointer. The array length is typically passed as a separate argument.

```
#include <stdio.h>

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

    printf("n");
}

void updateArray(int arr[], int size)
{
    for (int i = 0; i < size; i++)
    {
        arr[i] *= 2;
    }
}

int main(void)
{
    int numbers[] = {10, 20, 30, 40};
    int size = sizeof(numbers) / sizeof(numbers[0]);

    printf("Original array: ");
    displayArray(numbers, size);

    updateArray(numbers, size);

    printf("Updated array: ");
    displayArray(numbers, size);

    return 0;
}
```

### Example Output

```
Original array: 10 20 30 40
Updated array: 20 40 60 80
```

### Explanation

The function parameter:

```
void displayArray(const int arr[], int size)
```

accepts an array's elements for reading. In a function parameter list, `const int arr[]` is adjusted to `const int *arr`. The `const` qualifier prevents modification of the elements through this parameter.

The function:

```
void updateArray(int arr[], int size)
```

accepts a pointer to modifiable integers. The statement:

```
arr[i] *= 2;
```

updates the original array element because the pointer refers to the caller's array.

### Passing Arrays to Functions

| Parameter declaration | Meaning |
| --- | --- |
| `int arr[]` | Pointer to modifiable `int` elements |
| `const int arr[]` | Pointer to `const int` elements |
| `int arr[], int size` | Array access with an explicit element count |
| `int *arr` | Equivalent parameter type to `int arr[]` |

**Important:** The array's length is not automatically passed to the function. Inside `displayArray()` or `updateArray()`, `sizeof(arr)` gives the size of the pointer parameter, not the size of the original array. Passing the element count separately allows the function to iterate within the intended bounds.