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%d",&year,&month,&day);
      |         ^~~~~~~
      |         scanf
foo.c:8:36: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    8 |         if (month%400==0||year%4==0&&year%100!=0){
      |                           ~~~~~~~~~^~~~~~~~~~~~~
/nix/binutils-2.42/bin/ld: /tmp/cceMnlYE.o: in function `main':
foo.c:(.text.startup+0x42): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status