Constants are absolute values that are used in expressions and need to be defined in your C program using #define. Simple constants are decimal integers (such as 0, 1, 2). Constants that contain decimal points or the letter e are taken as floating point constants. As a convention, constants are typically declared using all capitals. For example, you may set the ID of a zone, or define constants YMIN and YMAX as shown below:

#define WALL_ID 5
#define YMIN 0.0
#define YMAX 0.4064