Answer:
#define:
A
#define instruction defines value to a symbolic constant for use in the
program. #define statement is a prepocessor compiler directive
which define a symbolic constant.
When the same value means different things in different places. We need
define a symbolic constant. Which has fixed value. This symbolic constant
defined by #define prepocessor directive.
Example:
#define
P1 3.14
#include:
C program are divided
into modules or functions. Some functions are written by users and many others
are stored in the C library. Library function has header files. If we want to
access the functions stored in the library, it is necessary to tell the
compiler about the files to be accessed. This is achieved by using the
preprocessor directive.
#include as follows
#include<filename>
filename is the name
of the library file that contains the required function definition preprocessor
directives are placed at the beginning of a program.