_ or __ in front of variables

[WanaGo]

Hello

Newbie question here - but I have noticed on a few peoples example programs, the use of _ or __ in front of some variables. I was just wondering what the purpose of these underscores is?

Do they serve a purpose, or are they just so the variables stand out or something?

Thanks

[PaulS]

Typically, the underscore is used in front of member variables in a class, to distinguish them (for the reader) from local variables. The presence or absence of the _ (or __) makes no difference to the compiler.

[WanaGo]

Thanks
So by 'member variables' you mean what I would call 'Global Variables' ?

As in variables that can be used throughout the sketch rather than local ones to a function.

Sorry coming from IEC PLC programming to this and still learning.

Since they have no effect to the compiler, that is good to know.

Thanks

[amacmullen14]

So by 'member variables' you mean what I would call 'Global Variables' ?

No, not at all, sorry.

What he means is variables that are part of a class.  
Not global, not local in a function, but in a separate class.