foo.cc: In function 'double multiplyAndDivision(std::__cxx11::string)':
foo.cc:80:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<a.size(); ++i) {
               ~^~~~~~~~~
foo.cc:92:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<a.size(); ++i) {
               ~^~~~~~~~~
foo.cc:95:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(; j<a.size(); ++j) {
          ~^~~~~~~~~
foo.cc: In function 'double addAndMinus(std::__cxx11::string)':
foo.cc:110:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<a.size(); ++i){
               ~^~~~~~~~~
foo.cc:121:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<a.size(); ++i) {
               ~^~~~~~~~~
foo.cc:124:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(; j<a.size(); ++j) {
          ~^~~~~~~~~
foo.cc: In function 'double bracket(std::__cxx11::string)':
foo.cc:138:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<a.size();++i){
              ~^~~~~~~~~
foo.cc: In function 'double calculate(double, std::__cxx11::string, char)':
foo.cc:73:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

[Hydro](https://hydro.ac)提供评测服务