/in/foo.cc: In function 'int gcd(int, int)':
/in/foo.cc:8:12: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
  while(r=a%b){
            ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:21:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=2;i<s.size();i++){
                ^