More Advanced Types of Definitions
A definition for a name can include more than a simple constant value. It can include an expression and, as you will see shortly, just about anything else!
The following defines the name TWO_PI as the product of 2.0 and 3.141592654:
#define TWO_PI 2.0 * 3.141592654
You can subsequently use this defined name anywhere in a program where the expression 2.0 * 3.141592654 would be valid. So, you could replace the return statement of the circumference method from the previous example with the following statement:
return TWO_PI * radius;
Whenever a defined name is encountered in an Objective-C program, everything that appears to the right of the defined name in the #define statement is ...
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