Caisar Cipher Text Matlab

CaisarCipher.m

alfabet = "abcdefghijklmnopqrstuvwxyz"
alfabet = [alfabet, upper(alfabet), ' ']
plain = 'Aku makan es krim'
plainafterdecode = ''
key = 33
cipher = ''
modulus = length(alfabet)

for plainsequence = 1:length(plain)
  for alfabetsequence = 1:length(alfabet)
    if plain(plainsequence) == alfabet(alfabetsequence)
      i = mod(alfabetsequence + key - 1, modulus) + 1
      cipher = [cipher, alfabet(i)]
    end
  end
end

for ciphersequence = 1:length(cipher)
  for alfabetsequence = 1:length(alfabet)
    if cipher(ciphersequence) == alfabet(alfabetsequence)
      i = mod(alfabetsequence - key - 1, modulus) + 1
      plainafterdecode = [plainafterdecode, alfabet(i)]
    end
  end
end

fprintf('%s -> %s -> %s \n', plain, cipher, plainafterdecode)