Solution to Lab 01 (#5)

labs/lab01.md

@@ -130,16 +130,14 @@ The number of digits can be computed by successive dividing the input number by
 the integer division, you can use the function `quotient`.
 :::
 
-<!--
 ::: details Solution
 ```scheme
 (define (num-of-digits n [acc 1])
- (cond [(< n 0) (num-of-digits (- n))]
- [(< n 10) acc]
- [else (num-of-digits (quotient n 10) (+ acc 1))]))
+ (define q (quotient n 10))
+ (if (= q 0) acc (num-of-digits q (+ acc 1))))
 ```
+Thank you for the improved solution <u>@Denis Pak</u>!
 :::
--->
 
 ### Task 2
 Write a function `(num->str n [radix 10])` taking as input an integer `n` together
@@ -159,7 +157,6 @@ remainders. The remainder after integer division can be computed by the function
 :::
 
 
-<!--
 ::: details Solution
 ```scheme
 (define (num->str n [radix 10])
@@ -174,18 +171,21 @@ remainders. The remainder after integer division can be computed by the function
  rem-str
  (string-append (num->str (quotient n radix) radix)
  rem-str)))
+```
 
-; Alternative
-#|
+Alternatively, you can use `string-ref` to pick out the correct character from `numeric-alphabet`
+given an index, and instead of `string-append`ing you can construct a list of characters which is
+converted to a string in the end:
+```scheme
 (define numeric-alphabet "0123456789ABCDEF")
+
 (define (num->char n [radix 10])
  (string-ref numeric-alphabet (remainder n radix)))
+
 (define (num->str n [radix 10] [acc '()])
  (cond
  [(negative? n) (num->str (- n) radix '(#\-))]
  [(< n radix) (list->string (cons (num->char n radix) acc))]
  [else (num->str (quotient n radix) radix (cons (num->char n radix) acc))]))
-|#
 ```
-:::-->
-
+:::