vector belongs to std namespace. You need to fully qualify its name as std::vector<int>.

I need to clarify that the C++ Standard allows you to use all options that JaredPar gave in his answer, but I would strongly recommend not to use using namespace std and especially in the header files. About using namespace std you can find well described opinion in this question. Personally I'm agree with it, so allow me to link it in my answer.

vector belongs to std namespace. You need to fully qualify its name as std::vector<int>.

I need to clarify that the C++ Standard allows you to use all options that JaredPar gave in his answer, but I would strongly recommend not to use using namespace std and especially in the header files. About using namespace std you can find well described opinion in this question. Personally I'm agree with it, so allow me to link it in my answer.

vector belongs to std namespace. You need to fully qualify its name as std::vector<int>

vector belongs to std namespace. You need to fully qualify its name as std::vector<int>.

I need to clarify that the C++ Standard allows you to use all options that JaredPar gave in his answer, but I would strongly recommend not to use using namespace std and especially in the header files. About using namespace std you can find well described opinion in this question. Personally I'm agree with it, so allow me to link it in my answer.