/in/foo.c: In function 'main':
/in/foo.c:5:2: warning: implicit declaration of function 'scanf_s' [-Wimplicit-function-declaration]
  scanf_s("%d", &x);
  ^~~~~~~
/in/foo.c:18:6: warning: statement with no effect [-Wunused-value]
   x3 == x3 + x1;
   ~~~^~~~~~~~~~
/tmp/ccQxYqQi.o: In function `main':
foo.c:(.text.startup+0x13): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status