foo.c: In function 'zhuanhuan':
foo.c:5:9: warning: implicit declaration of function 'binary' [-Wimplicit-function-declaration]
    5 |         binary(n / 2);
      |         ^~~~~~
/nix/store/j2gmfdd29cp3rcvghmn1a5kgcnmf8myp-binutils-2.40/bin/ld: /tmp/cclhZ6wW.o: in function `zhuanhuan':
foo.c:(.text+0xd): undefined reference to `binary'
collect2: error: ld returned 1 exit status

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