I want to use a variable named split_point inside a the substring function. I calculated the split point using these functions:

(list (substring num 0 split_point) (substring num split_point))

(define (log_2 decimal)
    (floor(/ (log decimal) (log 2))))

(define (find_size_in_byte num)
  (floor (+ 10 (log_2 num))))

When I try to use the split_point variable inside substring I get the error:
substring: contract violation
expected: exact-nonnegative-integer?
given: 2.0

I tried using **floor **inside the code:
`

(list (substring num 0 split_point) (substring num split_point))

I also tried to use exact and round but I couldn’t solve it.