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Comments

Comments are lines in the program that are used to inform yourself or others about the way the program works. They are ignored by the compiler, and not exported to the processor, so they don't take up any space on the Atmega chip.

Comments only purpose are to help you understand (or remember) how your program works or to inform others how your program works. There are two different ways of marking a line as a comment:

Example

 x = 5;  // This is a single line comment. Anything after the slashes is a comment 
         // to the end of the line

/* this is multiline comment - use it to comment out whole blocks of code

if (gwb == 0){   // single line comment is OK inside a multiline comment
x = 3;           /* but not another multiline comment - this is invalid */
}
// don't forget the "closing" comment - they have to be balanced!
*/

Tip
When experimenting with code, "commenting out" parts of your program is a convenient way to remove lines that may be buggy. This leaves the lines in the code, but turns them into comments, so the compiler just ignores them. This can be especially useful when trying to locate a problem, or when a program refuses to compile and the compiler error is cryptic or unhelpful.

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The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.