/in/foo.cc: In function 'int main()':
/in/foo.cc:18:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(!(c[i]>='a'&&c[i]<='z')&&i<c.size())cout<<c[i++];//我知道不用那么烦 但我太困了awa 
                                  ~^~~~~~~~~
/in/foo.cc:19:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(i>=c.size())break;
      ~^~~~~~~~~~
/in/foo.cc:21:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(j<c.size())
         ~^~~~~~~~~
/in/foo.cc:30:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(j<c.size())cout<<c[j];
      ~^~~~~~~~~