foo.cc: In function 'bool operator<(const Day&, const Day&)':
foo.cc:10:40: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   10 |         return a.y < b.y || a.y == b.y && a.m < b.m || a.y == b.y && a.y == b.y && a.d < b.d;
      |                             ~~~~~~~~~~~^~~~~~~~~~~~
foo.cc:10:81: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   10 |         return a.y < b.y || a.y == b.y && a.m < b.m || a.y == b.y && a.y == b.y && a.d < b.d;
      |                                                        ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
foo.cc: In function 'int get_mouth(int, int)':
foo.cc:16:31: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   16 |                 if(y % 4 == 0 && y % 100 != 0 || y % 400 == 0) return 29;
      |                    ~~~~~~~~~~~^~~~~~~~~~~~~~~

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