foo.cc: In function 'int main()':
foo.cc:18:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i <= str.length(); i++)
                    ^
foo.cc:21:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(i == str.length() || str[i] == '+' || str[i] == '*')
        ^
foo.cc:26:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i != str.length())
         ^

自豪的采用 HydroJudger 进行评测(github.com/hydro-dev/HydroJudger)

{"receive":"2020-04-14T15:31:28.824Z","handle":"2020-04-14T15:31:28.824Z","cache_start":"2020-04-14T15:31:28.833Z","read_cases":"2020-04-14T15:31:29.816Z","judge":"2020-04-14T15:31:29.816Z","done":"2020-04-14T15:31:31.245Z"}