HiToRiGoTo

These provide a rapid way to "clip" out and insert code.

Consider;

     #define FIRST

    main()
    {
       int a, b, c;

#ifdef FIRST
      a=2; b=6; c=4;
#else
      printf("Enter a:");
      scanf("%d", &a);
   
      printf("Enter a:");
      scanf("%d", &a);

      printf("Enter a:");
      scanf("%d", &a);
#endif
      additonal code

Note that if FIRST is defined (which it is in the above) the values of a, b and c are hardcoded to values of 2, 6 and 4. This can save a lot of time when developing software as it avoids tediously typing everything in each and everytime you run your routine. When FIRST is defined, all that is passed to the compiler is the code between the #ifdef and the #else. The code between the #else and the #endif is not seen by the compiler. It is as if it were all a comment.

source: http://www.phanderson.com/C/preprocess.html

# posted by Ifte @ 7:58 PM