What is an identifier?. Give examples

Answer 1

It is a name used to identify a variable, function, class or any other user-defined item.
Valid identifiers can have A-Z,a-z,_,0-9
Also it should not start with a number.

Right->hi,b33r,o_o
Wrong->4rsenal,#nanm

Answer 2

For C++ you can get all Informations about identifier on the following page
https://msdn.microsoft.com/en-gb/library/565w213d.aspx#United Kingdom (English)