foo.c: In function 'y':
foo.c:5:17: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if (n % 4 == 0 && n % 100 != 0 || n % 400 == 0)
      ~~~~~~~~~~~^~~~~~~~~~~~~~~
foo.c: In function 'main':
foo.c:17:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d", &y1, &m1, &d1);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:18:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d", &y2, &m2, &d2);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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