Using a loop, define function num7s(n) in Java,
which takes an integer n and returns the number
of 7s in the usual (base 10) representation of n.
For example, num7s(2770) = 2 and num7s(99) = 0.
Assume that the argument and answer both have type
int.
(Hint. Successively divide the number by 10.
Remember that k % 10 is the rightmost digit of k,
and k/10 gives you the number that you get by removing
the rightmost digit from k.)