s = 'HELLO, I am not here. I WENT to tHe MaRKEt.'
s.upcase # => "HELLO, I AM NOT HERE. I WENT TO THE MARKET."
s.downcase # => "hello, i am not here. i went to the market."
s.swapcase # => "hello, i AM NOT HERE. i went TO ThE mArkeT."
s.capitalize # => "Hello, i am not here. i went to the market."