Why does my little code give me this warning

Question

why does the compiler give me a warning in line 17:

Object_OutherClass.Object_InnerClass.SetZwischenspeicher(17); 

It says:

C6001: Not initialized storage is being used.

If anyone could help me that would be so cool but pls dont say Im a Noob, im just learning

#include <iostream>
using namespace std;

class OutherClass {
 public:
  class InnerClass {
   private:
    double Zwischenspeicher;

   public:
    void SetZwischenspeicher(double zahl) { Zwischenspeicher = zahl; }
    double getZwischenspeicher() { return this->Zwischenspeicher; }
  } Object_InnerClass;
};
int main() {
  OutherClass Object_OutherClass;
  Object_OutherClass.Object_InnerClass.SetZwischenspeicher(17);
  std::cout << Object_OutherClass.Object_InnerClass.getZwischenspeicher()
            << std::endl;
  cin.get();
  return 0;
}