How do I declare a variable length array and initialize it to zero?

Question

int n;
scanf("%d",&n);
int arr[n];
arr[n]={0};

I want to initialize all elements to 0.

on compilation i get error "expected expression" at line 4 position 8.

I searched but found no method to do that.

Answer 1

VLAs (variable length arrays) can't be initialized.

You can instead use memset :

memset(arr, 0, sizeof arr);

Alternatively, you can use a fixed size array (eg int arr[25] = {0}; ) or dynamically allocated array (eg with calloc that zero initializes).

Answer 2

instead of

arr[n]={0};

you need to (assuming automatic variables)

in definition (assuming n is a constant expression):

int arr[n] = {0,};

or after definition

memset(arr, 0, n * sizeof(*arr));

or

for(size_t i = 0; i < n; i++) arr[i] = 0;

if n is a constant expression and the arr has static storage duration (is global or has static keyword before it) you do not have to do anything

Answer 3

6.7.9 Initialization
...
Constraints
...
3 The type of the entity to be initialized shall be an array of unknown size or a complete object type that is not a variable length array type.

^{C 2011 Online Draft}

Emphasis added. VLAs may not have an initializer as part of their definition. You will have to zero out the array after the declaration, either using memset or a loop as shown by others.