/in/foo.cc: In function 'int main()':
/in/foo.cc:6:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s.length();++i){
                ^
/in/foo.cc:21:22: warning: value computed is not used [-Wunused-value]
     if(s[i]=='z')s[i]=='a';
                      ^