foo.c: In function 'main':
foo.c:8:15: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if(year1%4==0&&year1%100!=0||year1%400==0)
     ~~~~~~~~~~^~~~~~~~~~~~~~
foo.c:21:15: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if(year2%4==0&&year2%100!=0||year2%400==0)
     ~~~~~~~~~~^~~~~~~~~~~~~~
foo.c:35:12: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   if(i%4==0&&i%100!=0||i%400==0)
      ~~~~~~^~~~~~~~~~
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d%d%d%d",&year1,&month1,&day1,&year2,&month2,&day2);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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