foo.cc: In function 'int main()':
foo.cc:22:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |     for (int i = 0; i < input.length() - 1; i++)
      |                     ~~^~~~~~~~~~~~~~~~~~~~
foo.cc:37:5: error: 'vector' was not declared in this scope
   37 |     vector<string> output;
      |     ^~~~~~
foo.cc:5:1: note: 'std::vector' is defined in header '<vector>'; did you forget to '#include <vector>'?
    4 | #include <algorithm>
  +++ |+#include <vector>
    5 | 
foo.cc:37:18: error: expected primary-expression before '>' token
   37 |     vector<string> output;
      |                  ^
foo.cc:37:20: error: 'output' was not declared in this scope
   37 |     vector<string> output;
      |                    ^~~~~~

[Hydro](https://hydro.ac)提供评测服务