/in/foo.c: In function 'main':
/in/foo.c:7:9: warning: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
         exit(0);
         ^~~~
/in/foo.c:7:9: warning: incompatible implicit declaration of built-in function 'exit'
/in/foo.c:7:9: note: include '<stdlib.h>' or provide a declaration of 'exit'