Initializing variable length array

VLAs cannot be initialized by any form of initialization syntax. You have to assign the initial values to your array elements after the declaration in whichever way you prefer.

C11: 6.7.9 Initialization (p2 and p3):

No initializer shall attempt to provide a value for an object not contained within the entity being initialized.

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.

You'll have to use memset:

memset(board, 0, sizeof board);