foldl() function at the top of the file is an instance of a fold. It takes an array of integers (and its size), an initial value, and a pointer to a function of two
ints that returns an
int. It iterates through the array, applying the function to
initial and the next element in the list, updating
initial each time.
Write a function
add such that
foldl(num, arr, 0, add) computes the sum of the
num integers in
main print out the result of that.