/in/foo.c: In function 'main':
/in/foo.c:17:14: warning: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
     int *a = malloc(n * sizeof(int));
              ^~~~~~
/in/foo.c:17:14: warning: incompatible implicit declaration of built-in function 'malloc'
/in/foo.c:17:14: note: include '<stdlib.h>' or provide a declaration of 'malloc'
/in/foo.c:28:13: warning: implicit declaration of function 'free' [-Wimplicit-function-declaration]
             free(a);
             ^~~~
/in/foo.c:28:13: warning: incompatible implicit declaration of built-in function 'free'
/in/foo.c:28:13: note: include '<stdlib.h>' or provide a declaration of 'free'
/in/foo.c:40:5: warning: incompatible implicit declaration of built-in function 'free'
     free(a);
     ^~~~
/in/foo.c:40:5: note: include '<stdlib.h>' or provide a declaration of 'free'