title: Replacing every letter in a given string with the letter following in the alphabet
body: <p>I have to replace every letter in a string with the letter following it in the alphabet (i.e. <code>c</code> becomes <code>d</code>, <code>z</code> becomes <code>a</code>), capitalize every vowel (<code>a</code>, <code>e</code>, <code>i</code>, <code>o</code>, <code>u</code>), and return the modified string. I'm trying to find solutions without calling any functions like <code>sort</code> or <code>find</code>.</p>
  
  <p>I have this:</p>
  
  <pre><code>def LetterChanges(str)
    Changed_Letter = ""
    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]
    for i in 0..str.length do 
      if str[i] == 
      str[i] = alphabet[i] + 1 
    return str 
  end
  </code></pre>
  
  <p>but I am lost. Any help is appreciated.</p>