[c] warning: incompatible implicit declaration of built-in function ‘xyz’

Here is some C code that produces the above mentioned error:

int main(int argc, char **argv) {
  exit(1);
}

Compiled like this on Fedora 17 Linux 64 bit with gcc:

el@defiant ~/foo2 $ gcc -o n n2.c                                                               
n2.c: In function ‘main’:
n2.c:2:3: warning: incompatible implicit declaration of built-in 
function ‘exit’ [enabled by default]
el@defiant ~/foo2 $ ./n 
el@defiant ~/foo2 $ 

To make the warning go away, add this declaration to the top of the file:

#include <stdlib.h>