foo.cc: In function ‘int main()’:
foo.cc:9:18: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    9 |         if(y%4==0&&y%100==0||y%400==0)mon[2]=29;
      |            ~~~~~~^~~~~~~~~~
foo.cc:10:20: warning: ‘i’ is used uninitialized [-Wuninitialized]
   10 |         for(int i;i<m;i++)
      |                   ~^~
foo.cc:10:17: note: ‘i’ was declared here
   10 |         for(int i;i<m;i++)
      |                 ^