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C Programming: Visual Quickstart Guide by Marc Liyanage, Larry Ullman

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Using Constants

One of the classic tips for creating readable code is to avoid the use of magic tokens: literal values (such as a number) that are generally meaningless without some context. Here is an example of bad programming form:

if (num < 90) {
   // Do this.
}

Although you probably knew why num had to be less than 90 when you wrote the application, that's exactly the kind of thing you'll forget when revisiting the code some time later. Moreover, there's little chance of another programmer comprehending the meaning of that number.

A constant is a macro that defines a literal value. You can then use the constant whenever you would otherwise use the value. By using constants instead of literal values, you ensure that you or anyone else who ...

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