/in/foo.c: In function 'main':
/in/foo.c:20:5: warning: implicit declaration of function 'scanf_s' [-Wimplicit-function-declaration]
     scanf_s("%d", &n); 
     ^~~~~~~
/tmp/ccMUb0k3.o: In function `main':
foo.c:(.text.startup+0x29): undefined reference to `scanf_s'
foo.c:(.text.startup+0x89): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status