Question: I noticed that there is no reference to reference but there is pointer to pointer, and also there is no an array of references but an array of pointers.

Could anybody give me any reason?

Answer: 
It is according to C++ Standard 8.3.2/4:

> 
> There shall be no references to references, no arrays of references, and no pointers to references.
> 
> 
>
C++ Standard 8.3.2/4:

`There shall be no references to references, no arrays of references, and no pointers to references.`

The reasoning behind this is that a reference doesn't exist in and of itself at run-time. A reference merely is another name for a location. They are immutable.