foo.cc: In function 'int main()':
foo.cc:15:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < s.length(); ++i) {
                     ~~^~~~~~~~~~~~
foo.cc:24:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int j = 0; j < a.length(); ++j) {
                             ~~^~~~~~~~~~~~
foo.cc:27:38: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
                 else if (in == false && a[j] == '+' || a[j] == '-') {
                          ~~~~~~~~~~~~^~~~~~~~~~~~~~
foo.cc:38:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int j = 0; j < a.length(); ++j) {
                             ~~^~~~~~~~~~~~
foo.cc:41:38: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
                 else if (in == false && a[j] == '+' || a[j] == '-') {
                          ~~~~~~~~~~~~^~~~~~~~~~~~~~
foo.cc:52:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int j = 0; j < a.length(); ++j) {
                             ~~^~~~~~~~~~~~
foo.cc:55:38: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
                 else if (in == false && a[j] == '+' || a[j] == '-' || a[j] == '*' || a[j] == '/') {
                          ~~~~~~~~~~~~^~~~~~~~~~~~~~
foo.cc:14:9: warning: unused variable 'n' [-Wunused-variable]
     int n = s.length();
         ^

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

正在同步测试数据，请稍后
{"receive":"2020-07-16T10:46:18.887Z","handle":"2020-07-16T10:46:18.915Z","cache_start":"2020-07-16T10:46:19.025Z","read_cases":"2020-07-16T10:46:19.694Z","judge":"2020-07-16T10:46:19.700Z","done":"2020-07-16T10:46:21.869Z"}