/in/foo.cc:1:20: warning: extra tokens at end of #include directive
 #include <iostream>;
                    ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:8:40: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
  for(i=1;i<=n;i++) for(j=1;j<=n;j++) if(j%i==0) if(l[j-1]==true) l[j-1]=false;else l[j-1]=true;
                                        ^