foo.cc: In function 'int year(int, int)':
foo.cc:6:14: warning: statement has no effect [-Wunused-value]
    6 |         for (year1; year1 < year2; year1++)
      |              ^~~~~
foo.cc: In function 'int month(int, int)':
foo.cc:26:14: warning: statement has no effect [-Wunused-value]
   26 |         for (month1; month1 < month2; month1++)
      |              ^~~~~~

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