gsub with block

Explanation

In the given Ruby code, the gsub method is used to perform substitutions in a string.

Let's break down each line of code and explain the return values:

1. "aaoo".gsub("a") { |c| c.upcase }: This line of code replaces each occurrence of the substring "a" in the original string "aaoo" with the result of the block provided, which converts the matched character c to its uppercase equivalent. In this case,"a" is replaced with "A", and the result is "AAoo".

2. "aaoo".gsub("a", "o") { |c| c.upcase }: Similar to the first line, this code replaces each occurrence of the substring "a" in the original string "aaoo", but with the second argument "o" instead of a block. The block is still provided but is not used since a replacement string is given. Therefore, every "a" is replaced with "o", resulting in "oooo".

So, the return values for the two lines are as follows:

1. The first line returns the string "AAoo".
2. The second line returns the string "oooo".

Voilà!