20250627 16:00 If's

                                      

← Previous

🏠 Homepage

Next Chapter →

                                         

#if & #elif – If your code has trust issues...

Think of #if like a “bouncer” at a party:
"If the condition is true, you can enter this part of the code."

#if AGE >= 18
  printf("Welcome to the party!\n");
#else
  printf("Go back to school, kid!\n");
#endif

You can also do:

#if LEVEL == HARD || MODE == CRAZY
  // Challenge accepted
#endif

Use #elif to make it fancier:

#if ADAPTER == VGA
  // VGA code
#elif ADAPTER == SVGA
  // SVGA code
#else
  // Potato mode (EGA)
#endif

#elif = fewer #endifs = cleaner code = less headache!

#undef – Break with a macro

If you don't want to use a macro anymore (maybe it's being annoying), just do:

#undef PI

Now PI is no longer defined. Like a ghosted ex—poof, gone! 

#pragma – Secret commands to your compiler

Think of #pragma like whispering to the compiler:
"Hey... do something cool (or weird)."

#pragma startup and #pragma exit

They let you run special functions before and after main().

#pragma startup fun1
#pragma exit fun2

void fun1() { printf("Warming up...\n"); }
void fun2() { printf("Shutting down...\n"); }

void main() {
  printf("Main program running!\n");
}

Output:

Warming up...
Main program running!
Shutting down...

Note: The startup function runs before main(), and the exit function runs after it ends. Like putting on shoes before going out—and taking them off after coming back.

#pragma warn – Mute those annoying warning messages

Example:

#pragma warn -rvl // suppress return value warning
#pragma warn -par // suppress unused parameter warning
#pragma warn -rch // suppress unreachable code warning

Now even if you write messy code, compiler will say:
“I saw nothing.”

But don’t do this forever—it’s like ignoring a leaky tap. One day… 

Wrap-Up !

Directive	What It Does
#if, #elif, #else, #endif	Chooses which code to compile
#undef	Erases a macro
#pragma	Sends special instructions to the compiler (e.g., startup, exit, suppress warnings)

The preprocessor is like a code genie – it grants your wishes before compilation even begins. 
Use its powers wisely, and it’ll make your coding life a lot more magical.

Need the last part of the chapter? Just shout "abracadabra"!