Chapter 1 Task 9 question

[RazzorLabs]

Hi,

So I am trying to figure out how to solve this. I am able to sum all digits:

sumLastTwo 0 = 0 sumLastTwo x = (x mod10) + sumLastTwo (xdiv 10)

With mod I can get last digit, but how to take number before the last one?
I have tried to break digit in to the characters but no idea how to work with output afterwards.

[RazzorLabs]

I think I got it:

sumLastDigits x = let lastDigit = mod x 10 lastTwoDigits = mod x 100 in lastDigit + (lastTwoDigits div 10)

[chshersh]

@RazzorLabs Yes, that looks like a correct solution 🙂
Happy to see that you've figured it out! 👏🏻

[RazzorLabs]

I am fighting with Task 10 in Chapter 1. I have came with one idea how to do it. So I would like to split number on digits with:

splitToDigits n | n < 1 = [] | otherwise = splitToDigits (div n 10) ++ [mod n 10]

After that I would like to apply "head" on the list of char which should be working:

*Main> head [1, 4, 5]
1
*Main>

but I have no idea how to filter the ouptut using the head in the function which I have created. I know this is probably not the best solution but how can I do it this way?

thx

[chshersh]

@RazzorLabs I'm not sure I understand your question. But if you write a separate function splitDigits with the type Integer -> [Integer] as you described, you should be able to call head on the result of this function, i.e.

firstDigit :: Integer -> Integer
firstDigit n = head (splitDigits n)

[RazzorLabs]

Ouch. Nice. This is exactly what I was looking for. Thank you very much for the help. In the meantime I have found another way how to solve this. btw, thank you for this course, it is really amazing :)