What is a magic number, and why is it bad?

I just have a Numbers class I import into all my projects:<p>public final static int ZERO = 0; public final static int ONE = 1; public final static int TWO = 2; public final static int THREE = 3; public final static int FOUR = 4; ....<p>(jk)

The primary purpose of the DATA statement is to give names to constants; instead of referring to pi as 3.141592653589793 at every appearance, the variable PI can be given that value with a DATA statement and used instead of the longer form of the constant.<p>This also simplifies modifying the program, should the value of pi change.<p>-- Early FORTRAN manual for Xerox Computers

No one seems to be mentioning another use of the phrase &quot;magic number&quot; which isn&#x27;t bad at all - numbers put in files to mark the file type. 0xCAFEBABE in java class files, for instance.

That is about the worst top-rated answer I&#x27;ve seen in a while on SO.

I&#x27;d have personally thought the number used in the fast inverse square root (<a href="http://en.wikipedia.org/wiki/Fast_inverse_square_root" rel="nofollow">http:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Fast_inverse_square_root</a>) would qualify as a &#x27;magic number&#x27;, everything else is just a hardcoded value.

I find these a lot with CSS - banishing them seem to be a major goal of LESS, SASS etc.<p>They also seem to crop up too often in JS &#x2F; JQuery, particularly the manipulation of CSS.. where do you folks tend to find them?

Also, it can be a good idea to yank out all of those into a separate config file. Although, it destroys locality, so it depends on the use case I guess.

New term added to my vocabulary - thanks for sharing!

I just call any constants that slip into my code &quot;advanced technology numbers&quot; if someone gives me a hard time about them.

Caring about magic numbers is a distraction from real problems, such as getting your software working.