/in/foo.cc: In function 'int main()':
/in/foo.cc:17:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s3.length();i++)if(i!=s1.length()-1&&i!=s1.length())cout<<s3[i]; 
              ~^~~~~~~~~~~~
/in/foo.cc:17:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s3.length();i++)if(i!=s1.length()-1&&i!=s1.length())cout<<s3[i]; 
                                   ~^~~~~~~~~~~~~~~
/in/foo.cc:17:54: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s3.length();i++)if(i!=s1.length()-1&&i!=s1.length())cout<<s3[i]; 
                                                     ~^~~~~~~~~~~~~