Data Parallelism

Can I use array notations in programs without starting up the Cilk runtime?

Yes. Array notations in Cilk Plus are implemented as part of the compiler (i.e., ICC/ICL or GCC), and can be used even if your program does not use any Cilk keywords.

How do I choose between #pragma simd and array notation?

Use #pragma simd if you need your code compile with a non-Cilk Plus enabled compiler, which will just ignore the pragma. Otherwise consider using array notation if you like its array-oriented style of expression. Elemental functions can be used either way since their markup can be safely ignored.