/in/foo.c: In function 'main':
/in/foo.c:6:2: warning: implicit declaration of function 'scanf_s' [-Wimplicit-function-declaration]
  scanf_s("%d %d",&x1,&x2);
  ^~~~~~~
/in/foo.c:20:2: warning: 'y1' may be used uninitialized in this function [-Wmaybe-uninitialized]
  printf("%d %d",y1,y2);
  ^~~~~~~~~~~~~~~~~~~~~
/tmp/ccenhv0O.o: In function `main':
foo.c:(.text.startup+0x19): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status