foo.c: In function 'main':
foo.c:5:9: warning: zero-length gnu_printf format string [-Wformat-zero-length]
    5 |  printf("");
      |         ^~
foo.c:19:24: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   19 |   case 2:if((year%4==0)&&(year%100!=0)||year%400==0){
      |             ~~~~~~~~~~~^~~~~~~~~~~~~~~
foo.c:6:4: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    6 |    scanf("%d%d",&year,&month);
      |    ^~~~~~~~~~~~~~~~~~~~~~~~~~

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