View Compilation Error

0_0_14974932_7971.cpp: In constructor 'Graph::Graph()':
0_0_14974932_7971.cpp:17:5: error: uninitialized reference member in 'class std::vector<int>&' [-fpermissive]
     Graph(){
     ^
0_0_14974932_7971.cpp:28:18: note: 'std::vector<int>& Graph::V' should be initialized
     vector<int>& V;
                  ^
0_0_14974932_7971.cpp: In constructor 'Graph::Graph(int)':
0_0_14974932_7971.cpp:20:5: error: uninitialized reference member in 'class std::vector<int>&' [-fpermissive]
     Graph(int vCount){
     ^
0_0_14974932_7971.cpp:28:18: note: 'std::vector<int>& Graph::V' should be initialized
     vector<int>& V;
                  ^