foo.c: In function 'F':
foo.c:13:24: warning: 'return' with a value, in function returning void [-Wreturn-type]
   13 |                 return 0;
      |                        ^
foo.c:3:6: note: declared here
    3 | void F()
      |      ^
foo.c:27:16: warning: 'return' with a value, in function returning void [-Wreturn-type]
   27 |         return 0;
      |                ^
foo.c:3:6: note: declared here
    3 | void F()
      |      ^
foo.c: In function 'main':
foo.c:32:9: warning: implicit declaration of function 'scanf_s'; did you mean 'scanf'? [-Wimplicit-function-declaration]
   32 |         scanf_s("%d", &n);
      |         ^~~~~~~
      |         scanf
/nix/store/j2gmfdd29cp3rcvghmn1a5kgcnmf8myp-binutils-2.40/bin/ld: /tmp/ccrmxWL4.o: in function `main':
foo.c:(.text.startup+0x11): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status

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