/in/foo.c: In function 'main':
/in/foo.c:5:2: warning: implicit declaration of function 'scanf_s' [-Wimplicit-function-declaration]
  scanf_s(" %d",&n);
  ^~~~~~~
/tmp/ccBX3q0o.o: In function `main':
foo.c:(.text.startup+0x1c): undefined reference to `scanf_s'
foo.c:(.text.startup+0x46): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status