Ch 04

cc/ @fabioyamate @carlosgaldino.

Please review.
I think the idea of this exercise was not to use `&&` so you would need to use another `if`. Notice that on exercise 5 it mentions "and note the difference in the number of conditional expressions required".

Using `&&` only requires one `if` which is the same number of conditional expressions of exercise 5 which wouldn't make sense if the goal is to spot the difference between both versions.