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Changing the Case of a String
CodeExpectedActual
s = 'HELLO, I am not here. I WENT to tHe MaRKEt.'
s.upcase
 "HELLO, I AM NOT HERE. I WENT TO THE MARKET." "HELLO, I AM NOT HERE. I WENT TO THE MARKET." 
s.downcase
 "hello, i am not here. i went to the market." "hello, i am not here. i went to the market." 
s.swapcase
 "hello, i AM NOT HERE. i went TO ThE mArkeT." "hello, i AM NOT HERE. i went TO ThE mArkeT." 
s.capitalize
 "Hello, i am not here. i went to the market." "Hello, i am not here. i went to the market." 
un_banged = 'Hello world.'
un_banged.upcase
 "HELLO WORLD." "HELLO WORLD." 
un_banged
 "Hello world." "Hello world." 
banged = 'Hello world.'
banged.upcase!
 "HELLO WORLD." "HELLO WORLD." 
banged
 "HELLO WORLD." "HELLO WORLD." 
class String
  def capitalize_first_letter
    self[0].chr.capitalize + self[1, size]
  end
  def capitalize_first_letter!
    unless self[0] == (c = self[0,1].upcase[0])
      self[0] = c
      self
    end
    # Return nil if no change was made, like upcase! et al.
  end	
end
s = 'i told Alice. She remembers now.'
s.capitalize_first_letter
 "I told Alice. She remembers now." "I told Alice. She remembers now." 
s
 "i told Alice. She remembers now." "i told Alice. She remembers now." 
s.capitalize_first_letter!
s
 "I told Alice. She remembers now." "I told Alice. She remembers now." 
'LOWERCASE ALL VOWELS'.tr('AEIOU', 'aeiou')
 "LoWeRCaSe aLL VoWeLS" "LoWeRCaSe aLL VoWeLS" 
'Swap case of ALL VOWELS'.tr('AEIOUaeiou', 'aeiouAEIOU')
 "SwAp cAsE Of aLL VoWeLS" "SwAp cAsE Of aLL VoWeLS"