virtual keyword has nothing to do with return type of a method. It only tells that the following method is virtual (you can skip virtual in subclasses).

Try this:
Qt Code: 
  1. #include <iostream>
  2.  
  3. class A
  4. {
  5.    public:
  6.       A() {}
  7.       void nonVirt() { std::cerr << "A::nonVirt()" << std::endl; }
  8.       virtual void virt() { std::cerr << "A::virt()" << std::endl; }
  9.       virtual ~A() {}
  10. };
  11.  
  12. class B : public A
  13. {  
  14.    public:
  15.       void nonVirt() { std::cerr << "B::nonVirt()" << std::endl; }
  16.       void virt() { std::cerr << "B::virt()" << std::endl; }
  17. };
  18.  
  19. int main()
  20. {
  21.    A a;
  22.    B b;
  23.    A *ptr = &b;
  24.  
  25.    a.nonVirt();
  26.    a.virt();
  27.    b.nonVirt();
  28.    b.virt();
  29.    ptr->nonVirt();
  30.    ptr->virt();
  31.  
  32.    return 0;
  33. }
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