In HTML5 how to know the total number elements present in an array?

Question

Write a c program that rotate elements of an array by the value of configured number "n".
For example:
Input array[ ] = { 2, 3, 5, 6, 8, 9}
value of n = 2
Output array[] = { 5, 6, 8, 9, 2, 3}
I am looking for efficient program.