/in/foo.c: In function 'main':
/in/foo.c:7:18: warning: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
  int *a = (int *)malloc(sizeof(int)*n);
                  ^~~~~~
/in/foo.c:7:18: warning: incompatible implicit declaration of built-in function 'malloc'
/in/foo.c:7:18: note: include '<stdlib.h>' or provide a declaration of 'malloc'
/in/foo.c:33:2: warning: implicit declaration of function 'free' [-Wimplicit-function-declaration]
  free(a);
  ^~~~
/in/foo.c:33:2: warning: incompatible implicit declaration of built-in function 'free'
/in/foo.c:33:2: note: include '<stdlib.h>' or provide a declaration of 'free'