Macro Rules and Example

Macro without argument example

A #define directive is many a time used to define operators as shown below:

#include<stdio.h>
#define OR ||
#define AND &&
int main()
{
 int p=10,q=20,r=30;
 if((p==10) AND (q<25 OR r>=50))
    printf("You are winner!!");
 else
    printf("You are loser!!");
 getch();
 return 0;
}

The output of above program would be:

Figure: Screen shot of shows macro uses in C program

A #define directive could be used even to replace a condition as:


#include<stdio.h>
#define OR ||
#define AND &&
#define RESULT ((p==10) AND (q<25 OR r>=50))
int main()
{
 int p=10,q=20,r=30;
 if(RESULT)
    printf("You are winner!!");

 else
    printf("You are loser!!");
 getch();
 return 0;
}

The output of above program would be:

Figure: Screen shot of shows macro uses in C program

A #define directive could be used to replace even an entire C statement.

#include<stdio.h>
#define DISPLAY printf("Yes, I got iT");
int main()
{
 DISPLAY;
 getch();
 return 0;
}

The output of above program would be:

Figure: Screen shot for macro example C program

Macro with argument example

#include<stdio.h>
#define SQUARE(p) (p*p)
int main()
{
 int n,result;
 printf("Enter any number: ");
 scanf("%d", &n);
 result = SQUARE(n);
 printf("Square of %d is %d",n,result);
 getch();
 return 0;
}

The output of above program would be:

Figure: Screen shot of macro square C program

Keep in mind some following point, when you create macro

1. If there are two or more macro expansions then, entire macro expansions should be enclosed within parentheses.

Example:

#define SQUARE(p) p*p  //wrong 

#define SQUARE(p) (p*p)  //right

2. There should be not a blank between the macro template and its argument while defining the macro.

Example:

#define SQUARE (p) p*p  //wrong 

#define SQUARE(p) (p*p)  //right

3. Macro can be split into multiple lines, with a '\'(back slash) present at the end of each line.

Example:

#include<stdio.h>

#define MYPROG for(c=1; c<=10; c++)        \

               {                           \

                if(c==5)                   \

                   printf("Good C blog."); \

               }

int main()

{

 int c;

 MYPROG

 getch();

 return 0;

}

The output of above program would be:

Figure: Screen shot for macro split C program

Related article:

1. What is macro or macro expansion
2. String pyramid using macro