/in/foo.cc: In function 'int rn(int)':
/in/foo.cc:13:17: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   13 |  if (a % 4 == 0 && a % 100 != 0 || a % 400 == 0) return 1;
      |      ~~~~~~~~~~~^~~~~~~~~~~~~~~