/in/foo.c: In function 'main':
/in/foo.c:24:3: warning: implicit declaration of function 'free' [-Wimplicit-function-declaration]
   free(s[i]);
   ^~~~
/in/foo.c:24:3: warning: incompatible implicit declaration of built-in function 'free'
/in/foo.c:24:3: note: include '<stdlib.h>' or provide a declaration of 'free'
/in/foo.c:24:8: warning: passing argument 1 of 'free' makes pointer from integer without a cast [-Wint-conversion]
   free(s[i]);
        ^
/in/foo.c:24:8: note: expected 'void *' but argument is of type 'int'