Strings for Experts

This page contains information about advanced topics that I have been asked.

Randomizing Letters of a String

The implode and explode functions change strings to and from lists of single letters. To randomize a list, import racket/list and then use the shuffle function. If you are actually looking at lists, you should change to Beginning Student with List Abbreviations.

(require picturing-programs)
(require racket/list)
(define (mix letters)
  (implode
   (shuffle
    (explode letters))))
(mix "alphabet soup")

Advanced String Making

• There is an optional second argument to number->string that is the base to work in. (check-expect (number->string 31 2) "11111")

• Single characters are different from single letter words. Racket uses #\a to denote the character “a” and "a" to denote the word containing a single letter a. Usually you do not work with characters, but…

• The make-string command takes in a number and a character to repeat (meaning #\a not "a"). Example: (check-expect (make-string 7 #\a) "aaaaaaa").

• The replicate command repeats a string a certain number of times. Example: (check-expect (replicate 2 "moo") "moomoo").