please explain why / * 1 * / is hidden for what it is not shown in the line

Answer 1

that is a multiline comment tag you have the 1 surrounded in. The number 1 will not be seen by the compiler.

Answer 2

actually when compiler compiles program then when he see /* then it ignores text until */ this is an multi line comment

Answer 3

Because the preprocesser deleted it before the compiler even gets the code