Add Use A Case Statement As A Cond Statment as a ruby til

ruby/use-a-case-statement-as-a-cond-statement.md

@@ -0,0 +1,29 @@
+# Use A Case Statement As A Cond Statement
+
+Many languages come with a feature that usually takes the name _cond
+statement_. It is essentially another way of writing an _if-elsif-else_
+statement. The first conditional in the _cond statement_ to evaluate to try
+will then have its block evaluated.
+
+Ruby doesn't have a _cond statement_, but it does have a _case statement_.
+By using a _case statement_ with no arguments, we get a _cond statement_. If
+we exclude arguments and then put arbitrary conditional statements after the
+`when` keywords, we get a construct that acts like a _cond statement_. Check
+out the following example:
+
+```ruby
+some_string = "What"
+
+case
+when some_string.downcase == some_string
+  puts "The string is all lowercase."
+when some_string.upcase == some_string
+  puts "The string is all uppercase."
+else
+  puts "The string is mixed case."
+end
+
+#=> The string is mixed case.
+```
+
+[source](http://www.skorks.com/2009/08/how-a-ruby-case-statement-works-and-what-you-can-do-with-it/)