/in/foo.cc: In function 'int main()':
/in/foo.cc:58:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s.length();++i)s[i]=tolower(s[i]);
               ~^~~~~~~~~~~
/in/foo.cc:68:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s1.length();++i)s1[i]=tolower(s1[i]);
               ~^~~~~~~~~~~~
/in/foo.cc:69:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s1.length();++i)s2[i]=tolower(s2[i]);
               ~^~~~~~~~~~~~