/in/foo.c: In function 'main':
/in/foo.c:10:2: warning: implicit declaration of function 'scanf_s' [-Wimplicit-function-declaration]
  scanf_s("%" PRIu32, &k);
  ^~~~~~~
/in/foo.c:15:15: error: 'i' undeclared (first use in this function)
   Sn += 1.0 / i;
               ^
/in/foo.c:15:15: note: each undeclared identifier is reported only once for each function it appears in