Re: [racket-users] Racket program that finds the number of sym bols, the number of numerical characters and the number of alphabetical characters in an inp ut string.

[Matthias Felleisen]

On Nov 16, 2015, at 2:58 PM, Merve Tektaş <mervetektas1...@gmail.com> wrote:

> 
> Example Output:
> “PsPe4-3 ds** 9kKt??” 
> numbers: 3
> symbols: 5
> letters: 9
> 
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Here is your homework solution: 

#lang htdp/isl

(define DIGITS (explode "0123456789"))
(define SYMBOLS (explode "?!@#$%^&*()-"))
(define LETTERS
  (append
   (explode "qwertyuiopasdfghjklzxcvbnm")
   (explode "QWERTYUIOPASDFGHJKLZXCVBNM")))

;; String -> [List N N N]
;; count how often a DIGIT SYMBOL or LETTER appears in this string (str)

(check-expect (main "PsPe4-3 ds** 9kKt??") (list 3 5 9))

(define (main str)
  (local ((define exp (explode str)))
    (list (count exp DIGITS) (count exp SYMBOLS) (count exp LETTERS))))

;; [Listof 1String] [Listof 1String] -> N
;; count how often a member of s appears in this string (str)

(define (count str s)
  (cond
    [(empty? str) 0]
    [else (local ((define result (count (rest str) s)))
            (if (member? (first str) s) (add1 result) result))]))


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