foo.cc: In function 'int up(int)':
foo.cc:9:1: warning: control reaches end of non-void function [-Wreturn-type]
    9 | }
      | ^
foo.cc: In function 'int down(int)':
foo.cc:15:1: warning: control reaches end of non-void function [-Wreturn-type]
   15 | }
      | ^

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