Thats because u put the value of a into a thats why. Luk at ur 3rd statement...
If u put a = a and then print a and a, ur output will be 1.1 1.1 !! I think u shud read up on arrays !!
First, a lil bit of history and theory: since C++ is based on C, and C is a pretty low-level language, many things are closer to how computer does them, then they are to human's way.
Arrays (or container) indexing is one such case.
They are indexed beginning at 0 (so you used them properly in the cout statements), so a statement like yours a=a; actually assigns the second element the same value as the third one.