The algorithm occur(a, f, l, x) below returns the number of occurrences of x in array a between positions f and l. More precisely, it satisfies the following precondition/postcondition pair:

a) Implement the occur algorithm in the specified programming language
b) Define the preconditions and postconditions of the algorithm
c) Test the algorithm with various inputs to ensure correctness
d) Document the algorithm's behavior and usage guidelines