foo.cc: In function 'int runnian(int)':
foo.cc:5:17: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
    5 |  if (y % 4 == 0 && y % 100 != 0 || y % 400 == 0)
      |      ~~~~~~~~~~~^~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:43:5: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   43 |  if (y1 < y2)
      |     ^
foo.cc:49:5: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   49 |  if (y1 < y2)
      |     ^
foo.cc: In function 'int movedays(int, int, int)':
foo.cc:28:1: warning: control reaches end of non-void function [-Wreturn-type]
   28 | }
      | ^
foo.cc:15:12: warning: 'moveday' is used uninitialized in this function [-Wuninitialized]
   15 |    moveday += 31;
      |    ~~~~~~~~^~~~~

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