foo.cc: In function 'int trans(std::__cxx11::string)':
foo.cc:24:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<str.length();i++)
              ~^~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:49:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<str.length();i++)
              ~^~~~~~~~~~~~~
foo.cc: In function 'int cal(int, int, char)':
foo.cc:38:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

自豪的采用jd5进行评测(github.com/masnn/jd5)