Either that or it should be declared with no size at all:
This will create an error as the compiler will not be able to determine how much memory to allocate. You must declare a constant value for the size of the ray in the declaration statement.
NOTE: The elements field within brackets  which represents the number of elements the array is going to hold, must be a constant value, since arrays are blocks of non-dynamic memory whose size must be determined before execution. In order to create arrays with a variable length dynamic memory is needed, which is explained later in these tutorials.