Defining Macros

Example 1
#include <stdio.h>

#define SUM a+b    // Macros used just to replace values .
                                        // Whenever compiler see 'SUM' keyword in the program      
                                       //  it will replaced with a+b .

                                       //  It works on the principal of function, so you don't have to
                                       //  write same long particular statement every where in the program 
                             

int main (){

   int a = 5,
       b = 3,
       c;             

   c = SUM - 1;     // this statement is same as c = a + b - 1;
   printf("%d", c);

   return 0;

}

　



Example 2
 #include <stdio.h>

#define SUM(a,b) (a+b)  // Macros look for each and every word or symbol
                        // So,  here SUMa,b would not work. 

#define MAX(a,b) (((a)>(b))?(a):(b))  // Also, it is not different than..
                        // MAX(a,b) (a>b ) ? (a:b)
                   // However, they are placed in brackets to
                   // avoid mathematical errors in complex equations
                 
int main (){

  int x = 5,
      y = 3,
      z, h;

  z = SUM(x,y) - 1;    // same as functions.. x => a and y => b
                       // SUM(x --> a, y--> b) = SUM (a,b)..
                       // replace with  a + b ==> x + y
  printf("%d",z);

  h = MAX(x+y,z*x);    //i.e. MAX (x + y --> a, z * x --> b)
                              MAX (8, 35) ==> (8>35) ? (8:35) 
  printf("%d",h);     // of course statement is false so .. 35 is returned        

  return 0;

}