Using the #define method of declaring a constant enables you to declare a constant
in one place and use it throughout your program. This helps make your programs more
maintainable, because you need to maintain only the #define statement and not several
instances of individual constants throughout your program.
For instance, if your program used the value of pi (approximately 3.14159) several
times, you might want to declare a constant for pi as follows:
#define PI 3.14159
Using the #define method of declaring a constant is probably the most familiar way
of declaring constants to traditional C programmers. Besides being the most common
method of declaring constants, it also takes up the least memory. Constants defined
in this manner are simply placed directly into your source code, with no variable
space allocated in memory. Unfortunately, this is one reason why most debuggers
cannot inspect constants created using the #define method.