/in/foo.cc: In function 'int main()':
/in/foo.cc:6:7: warning: statement has no effect [-Wunused-value]
  for(a;a<=b;a++){
       ^
/in/foo.cc:7:12: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   if(a%4==0&&a%100!=0||a%400==0){
      ~~~~~~^~~~~~~~~~