C++运算符重载错误C44 30:缺少类型说明符-int假设

Visual studio给出了此错误:

Error   1   error C4430: missing type specifier - int assumed. Note: C++ does not support default-int   c:\users\johnny\documents\visual studio 2010\projects\stack_linkedlist\stack_linkedlist\classstack.cpp  111 1   STACK_LinkedList

它指向我的运算符重载函数。这是我的操作员超载的代码。

//operator overload
template <class S>
const Stack<S>::operator=( const Stack& s )
{
    // Check for self assignment
    if (&s==this)
        return *this;

    // Clear the current stack
     while (s.theFront)
        {
            NodePointer p = s.theFront;

            s.theFront = s.theFront->next;
            delete p;
        }

        s.theTop = s.theFront;


    // Copy all data from stack s
    if (!s.isEmpty())
    {
        NodePointer temp = q->theFront;

        while(temp != 0)
        {
            push(temp->data);
            temp = temp->next;
        }
    }

   return *this;
}