/in/foo.cc: In function 'int main()':
/in/foo.cc:18:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<num.length();i++){
          ~^~~~~~~~~~~~~
/in/foo.cc:28:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  else if(num.length()-i<n){
          ~~~~~~~~~~~~~~^~
/in/foo.cc:30:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(;i<num.length();i++){
        ~^~~~~~~~~~~~~