10.3.1.1 Scoping Rules: Private and Shared

A private variable or array is private to a single iteration of a loop. The value assigned to a private variable or array in one iteration is not propagated to any other iteration of the loop.

A shared variable or array is shared with all other iterations. The value assigned to a shared variable or array in an iteration is seen by other iterations of the loop.

If an explicitly parallelized loop contains shared references, then you must ensure that sharing does not cause correctness problems. The compiler does not synchronize on updates or accesses to shared variables.

If you specify a variable as private in one loop, and its only initialization is within some other loop, the value of that variable may be left undefined in the loop.