Question: What is difference between 

```
int x=7;

```

and 

```
register int x=7;

```

?

I am using C++.

Answer: 
`register` is deprecated in C++11. It is unused and reserved in C++17.

Source: <http://en.cppreference.com/w/cpp/keyword/register>
Almost certainly nothing.

`register` is a hint to the compiler that you plan on using `x` a lot, and that you think it should be placed in a register.

However, compilers are now far better at determining what values should be placed in registers than the average (or even expert) programmer is, so compilers just ignore the keyword, and do what they wants.