What is “##” operator in C?

Answer 1

## is an macro operator which is used to concatenate
https://www.cprogramming.com/reference/preprocessor/token-pasting-operator.html

Answer 2

The ‘##’ pre-processing operator performs token pasting. When a macro is expanded, the two tokens on either side of each ‘##’ operator are combined into a single token, which then replaces the ‘##’ and the two original tokens in the macro expansion.

Answer 3

This is given in the SL C tutorial BTW.

Answer 4

It is a macro-operator that is used to concatenate

Answer 5

Macro token and concantenates 5 ## 6