How to get the rightmost digit from an Integer - Ruby
I am working on a program that requires me to read in and validate a number, but in doing so I need to take a two digit integer (for example we'll say 18) and add it 1 + 8. Now I have it working where I do a conditional check if it is greater than 10 and subtract, but that's kind of an ugly solution in my opinion and was wondering if there is a cleaner way of doing it?
Answer
You can use the modulo operator n % 10, to get the rightmost digit. For example:
18 % 10
# => 8
9 % 10
# => 9
0 % 10
# => 0
(-123).abs % 10
# => 3
To handle negative numbers, use Integer#abs.
EDIT
Ruby 2.4 has a Integer#digits method. It will give you the digits as an array, starting from unit's place. And if you want to add the digits, you can use Enumerable#sum.
123.digits
# =>[3, 2, 1]
123.digits.first
# => 3
123.digits.sum
# => 6