/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<s.size();i++)
                 ~^~~~~~~~~
/in/foo.cc:10:14: warning: array subscript has type 'char' [-Wchar-subscripts]
        c[s[i]]++;
              ^
/in/foo.cc:12:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<s.size();i++)if(c[s[i]]==1){ //s[i]出现的次数为1 
                 ~^~~~~~~~~
/in/foo.cc:12:41: warning: array subscript has type 'char' [-Wchar-subscripts]
     for(int i=0;i<s.size();i++)if(c[s[i]]==1){ //s[i]出现的次数为1 
                                         ^