foo.c: In function 'main':
foo.c:7:9: warning: implicit declaration of function 'scanf_s'; did you mean 'scanf'? [-Wimplicit-function-declaration]
    7 |         scanf_s("%d %d", &x1, &x2);
      |         ^~~~~~~
      |         scanf
foo.c:13:21: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   13 |                 if (a = 0) { break; }
      |                     ^
/nix/store/vhf2cr6immz4qdxd83y025fnxim8mmfg-binutils-2.38/bin/ld: /tmp/ccY13m43.o: in function `main':
foo.c:(.text.startup+0x18): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status

[Hydro](https://hydro.ac)提供评测服务