Caesar Cipher shift on a string using shifting number

Question

I have this question. Using the Ruby language, have the function CaesarCipher(str,num) take the str parameter and perform a Caesar Cipher shift on it using the num parameter as the shifting number. A Caesar Cipher works by shifting each letter in the string N places down in the alphabet (in this case N will be num). Punctuation, spaces, and capitalization should remain intact. For example if the string is "Caesar Cipher" and num is 2 the output should be "Ecguct Ekrjgt".

Any my code looks like this. I think the onlt problem i have is to update each letter and then each word within the loops. please help. thank you

def Caesar_cipher(str, num)
  if num > 25
    num -= 26
  end
  alphabet = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]
  str = str.split(" ")
  str.each do |word|
    word.each_char do |c|
      if alphabet.include?(c)
        n = alphabet.index(c) + num
        if n > 25
          n -= 26
        end
        c = alphabet[n]
      end
    end
  end
  return str
end

puts Caesar_cipher("zabcd", 1) // "zabcd"

c = alphabet[n] doesn't update the character, it just assigns to a local variable c that is never used. — Stefan
– Stefan, Commented Oct 13, 2014 at 12:48
You do not update str so can't expect it would contain the result. Enumerator#each* family methods return containing object, no block results. You may look for Enumerable#collect (#map) methods. Also condition to keep n in 0-25 boundary can be simply rewritten with modulo, like n %= 26. — David Unric
– David Unric, Commented Oct 13, 2014 at 12:53
Actually, I got it working with minor changes. Noticed some oddities: lowercase letters are not affected, splitting on spaces is not necessary (spaces are not in the alphabet, but block should be modified to return c in this case), use of each_char (could be chained like each_char.collect ... .join for gathering results). Shall I report my findings in more depth, or you'll figure this on your own? — D-side
– D-side, Commented Oct 13, 2014 at 13:03

Tesfa Zelalem · Accepted Answer · 2014-10-13 13:30:03Z

1

  str = str.split("")
  alphabet = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]
  alphabet2 = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
  while num > 25 
    num -= 26
    end

  str = str.map do |char|
    if alphabet.include?(char)
      n = alphabet.index(char) + num
      while n > 25
        n -= 26
        end
      char = alphabet[n]

     elsif alphabet2.include?(char)
       m = alphabet2.index(char) + num



      while m > 25
        m -= 26
        end
      char = alphabet2[m]
      else
       char

     end
    char
    end

  return str.join


end

edited Oct 13, 2014 at 13:30

answered Oct 13, 2014 at 13:06

Tesfa Zelalem

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3 Comments

D-side Over a year ago

This suffers from the same issue I mentioned above: it doesn't affect uppercase letters.

Tesfa Zelalem Over a year ago

I know, it doesn't. I was focusing on the main problem. sorry for not being detailed. It is updated now.

Stefan Over a year ago

@TesfaZelalem you can use String#tr to replace characters, e.g.: "caesar cipher".tr(alphabet.join, alphabet.rotate(2).join)

Darkmouse · Accepted Answer · 2014-11-06 15:08:51Z

1

def cipher_shift(s, n)
  letters = [*'a'..'z'] 
  s.chars.map {|x| letters.include?(x.downcase) ? (x.ord + n).chr : x}.join
end

answered Nov 6, 2014 at 15:08

Darkmouse

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