The Preprocessor In C

The Preprocessor In C:-
The C Preprocessor is not a part of the compiler, but is a separate step in the
compilation process. In simple terms, a C Preprocessor is just a text substitution
tool and it instructs the compiler to do required preprocessing before the actual
compilation.
All Preprocessor commands begin with a hash symbol (#). It must be the first
nonblank character, and for readability, a preprocessor directive should begin in
the first column Of Program
Some Of Preprocessors Are:-
#define :-Substitutes a preprocessor macro.
#include:-Inserts a particular header from another file.
#undef:-  Undefines a preprocessor macro.
#ifdef:-  Returns true if this macro is defined.
#ifndef:- Returns true if this macro is not defined.
#if:-     Tests if a compile time condition is true.
#else:-   The alternative for #if.
#elif :-  #else and #if in one statement.
#endif:-  Ends preprocessor conditional.
#error:-  Prints error message on stderr.
#pragma:- Issues special commands to the compiler,using a Stander 
Let Us Take A Program To Understand By A Program:-
#include <stdio.h>
int main()
{
printf("File_Name_Is:%s\n", __FILE__ );
printf("Date Is :%s\n", __DATE__ );
printf("Now_Time Is:%s\n", __TIME__ );
printf("Line :%d\n", __LINE__ );
printf("ANSI :%d\n", __STDC__ );
return 0;
}
Another Program On #define Preprocessor
#include <stdio.h>
#define MAX(x,y) ((x) > (y) ? (x) : (y))
int main(void)
{
printf("Max between 30 and 20 is =%d\n", MAX(30, 20));
return 0;
}


Note:-
1.One of the powerful functions of the CPP is the ability to simulate functions using

parameterized macros.
Example:-#define square(y) ((y) * (y))

2.If the specified identifier is defined, the

value is true (non-zero). If the symbol is not defined, the value is false (zero).


                                                       Thanks, A Lot:-