foo.c: In function ‘main’:
foo.c:8:19: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    8 |         if (y%4==0&&y%100!=0||y%400==0)
      |             ~~~~~~^~~~~~~~~~
foo.c:92:10: warning: ‘days’ may be used uninitialized [-Wmaybe-uninitialized]
   92 |          printf("%d",days);
      |          ^~~~~~~~~~~~~~~~~
foo.c:4:15: note: ‘days’ was declared here
    4 |     int y,m,d,days;
      |               ^~~~