/in/foo.c: In function 'main':
/in/foo.c:16:2: warning: implicit declaration of function 'scanf_s' [-Wimplicit-function-declaration]
  scanf_s("%d", &n);
  ^~~~~~~
/in/foo.c:15:22: warning: unused variable 'j' [-Wunused-variable]
  int a[10000], n, i, j;
                      ^
/tmp/ccohngS9.o: In function `main':
foo.c:(.text.startup+0x1c): undefined reference to `scanf_s'
foo.c:(.text.startup+0x49): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status