get the flip side with index.


# It returns the index of the first element that matches the object:

q1 = %w[ January February March ]
q1.index "March" # => 2

1.	Elements can be accessed by their index (their position within the array).
2.	The first element in the array corresponds to array index 0, not 1,
3.	Use negative array indices in Ruby.
4.	The last element in the array is -1, the previous one -2, the previous one -3
5.	Use a variable (or a constant) as an array index
6.	To change an element, you can simply assign it a new value or manipulate it
7.	Assign string value to an integer array
8.	Use while and array index to get element from an array
9.	Use until and array element to loop through an array
10.	Mix up an array

get the flip side with index. : Array Index « Array « Ruby