How to declare variable

Answer 1

Hello! Unfortunately, questions like yours do not really belong here, because the answers are in SoloLearn's courses. Please try learning a bit before you ask a question :). I recommend you to read the guidelines of the Q&A Section down below.
https://www.sololearn.com/Discuss/1316935/welcome-to-sololearn-forum/

Answer 2

I don't know

Answer 3

In C++
First specify the data type then give your variable a name. At last put a ; semicolon
Name of the variable can only begin with a alphabet not with numbers and special characters like &-+( etc.
You cannot make use of spaces in a variable.
Example
int num;

You can also initialize your variable at the time of declaration .
int num = 123;