/in/foo.c: In function 'main':
/in/foo.c:8:3: warning: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
   exit(0);
   ^~~~
/in/foo.c:8:3: warning: incompatible implicit declaration of built-in function 'exit'
/in/foo.c:8:3: note: include '<stdlib.h>' or provide a declaration of 'exit'