foo.c: In function 'leap':
foo.c:4:39: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if (year % 4 == 0 || year % 400 == 0 && year % 100 != 0)
                       ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
foo.c: In function 'main':
foo.c:15:6: warning: unused variable 't' [-Wunused-variable]
  int t, s, i, t1 = 0, n = 0, n2 = 365, n1 = 366;
      ^
foo.c:19:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d", &y1, &m1, &d1);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:21:2: 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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