Answer 1

This is because you are calling .index() on an array which only contains letters from lowercase 'a' till lowercase 'z', that is, the array does not have uppercase letters. Passing a letter to arrayofnums.index() that is not present in arrayofnums (like an uppercase letter) will return `nil`. When you use the + operator on nil, it gives error.

`word.downcase` does not work for you because the `String.downcase` method does NOT make changes to the original string, it instead *returns the downcased string*. Change the line 4 to
`word = word.downcase`
OR
`word.downcase!`