CODEWITHSUNDEEP
lisp
R.DM
R.DM

Reputation: 105

Number of digits in a number with lisp using cond

So, I know that there is a solution using the if statement which is the following

    (defun numdigits (n)
      (if (< -10 n 10)
         1
         (1+ (numdigits (truncate n 10)))))

But I'm trying to deepen my knowledge and to understand to go for transforming if statements to the cond statement. SO I tried it out using the cond statement, but I receive an error, and quite honestly, I don't know why.

Here's what I did:

    (defun nbDigits (digit)
     (cond 
          ((> 0 (- digit 10)) 1)
          (t (1 + (nbDigits (truncate digit 10))))
      )
     )

The logic I'm having is: If 0 is greater than x-10, return 1 ( as this means the number is smaller than 10). Else, return 1 + nbDigits(the quotient of the digit when it's divided by 10), which should go until it reaches the base case.

I'm getting the error: Illegal argument in functor position: 1 in (1 + (NBDIGITS (TRUNCATE DIGIT 10))). But I don't understand how to go about this error.. Did I do a wrong call? Thanks.

Upvotes: 0

Views: 1278

Answers (1)

Leo
Leo

Reputation: 1934

A simple space between 1 and + is changing the function 1+ into two elements. Remove that space and you are done.

Incidentally, simplify your math by writing (< digit 10) instead of (> 0 (- digit 10))

In the end it should look like this:

(defun nbDigits (digit)
     (cond 
          ((< digit 10) 1)
          (t (1+ (nbDigits (truncate digit 10))))
      )
     )

Upvotes: 3

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