foo.cc: In function 'bool check(int)':
foo.cc:7:14: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
     if(y%4==0&&y%100!=0||y%400==0){
        ~~~~~~^~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:13:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d%d",&y,&m,&d);
     ~~~~~^~~~~~~~~~~~~~~~~~~