/in/foo.cc: In function 'int main()':
/in/foo.cc:9:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<a.length();i++)a[i]=tolower(a[i]);
                 ~^~~~~~~~~~~
/in/foo.cc:10:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<b.length();i++)b[i]=tolower(b[i]);
                 ~^~~~~~~~~~~
/in/foo.cc:17:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         while(ba!=string::npos){
               ~~^~~~~~~~