C Language: Preprocessors

The statements starting with the special symbol # are known as preprocessors statements or preprocessor directives.

Preprocessor statements are processed before the program goes to the compiler for processing.

Using preprocessors following can be performed

  • Macro definitions
  • Macros with arguments
  • Conditional compilation
  • File inclusion

Macro definitions

  • “#define” statement helps us to define a macro.
  • Macro once defined becomes a constant.
  • Its value cannot be changed during the execution of the program.
  • If we try to change the value an error will get generated.
  • Macro definition is not terminated by semicolon.
  • Each macro name in the program is substituted by the macro value before the program goes to the compiler for compilation.

Example:

#define a 10
#define limit 100
#define num int
#define pi 3.1415

#define c clrscr()
#define p printf
#define g getch();

Question:
Which is better and why?

(a) #define pi 3.1415
(b) float pi=3.1415;

Ans:
(a) is better, as it becomes a symbolic constant its value cannot be changed during the execution of the program and if we try to change the value an error will get generated.

Example:1

#include<stdio.h>
#define limit 100
int main()
{
    int i;
    for(i=1;i<=limit;i++)
    {
        printf("%d ",i);
    }
    return(0);
}

Example:2

#include<stdio.h>
#include<conio.h>
#define p printf
#define s scanf
//#define c clrscr();
#define g getch()
#define num int
#define hello int
#define ankur main()

hello ankur
{
    num a,b;
    //c
    p("enter any number ");
    s("%d",&a);
    b=a*a;
    p("square is %d\n",b);
    g;
    return(0);
}
/* Output */
enter any number 2
square is 4

Example:3

#include<stdio.h>
#include<conio.h>
#define begin {
#define end }
#define bs (
#define be )
#define hello void
#define mukesh main
#define p printf("hello");
//#define c clrscr();
#define g getch();
hello mukesh bs be
begin
//c
p
g
end
/* Output */
hello

Example:4

#include<stdio.h>
#include<conio.h>
#define c {
#define g }
#define a void
#define b main()
#define e printf("Hello How are you");
//#define d clrscr();
#define f getch();
a b c //d
e f g
/* Output */
Hello How are you

Example:5

#include<stdio.h>
#include<conio.h>
#define a void
//#define b main(){clrscr();printf("hello");getch();}
#define b main(){printf("hello");getch();}
a b
/* Output */
hello

Example:6

#include<stdio.h>
#include<conio.h>
//#define a main(){clrscr();printf("hello");getch();return(0);}
#define a main(){printf("hello");getch();return(0);}
a
/* Output */
hello

C Language Programming Tutorial

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