/in/foo.cc: In function 'int main()':
/in/foo.cc:7:7: warning: statement has no effect [-Wunused-value]
  for(i;i<=a;i++)
       ^
/in/foo.cc:9:13: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   if(i%4==0 && i%100!=0 || i%400==0)
      ~~~~~~~^~~~~~~~~~~