error: 'template<class T> class Dynamic_Array' used without template parameters - c++

Question

I've been getting this error for some time, and I have no clue how to fix it.
I searched for similar problem here on stack overflow, but I've failed to find anything.
Source code:
template <typename T>
class Dynamic_Array
{
private:
T* actual_array;
unsigned int number_of_elements;
public:
Dynamic_Array() {}
~Dynamic_Array() {delete[] actual_array;}
unsigned int get_size() const {return number_of_elements;}
T& operator [](unsigned int index) {return actual_array[index];}
void operator +=(T&);
void operator -=(unsigned int);
};
template <typename T> /*Not sure if this is needed, but compiler doesn't mind, still prints the same error*/
void Dynamic_Array<T>::operator+=(T& object)
{
if(number_of_elements>1)
{
T* temp_array = new T[number_of_elements];
for(unsigned int i=0;i<number_of_elements;i++)
{
temp_array[i]=actual_array[i];
}
delete[] actual_array;
actual_array = new T[number_of_elements+1];
for(unsigned int i=0;i<number_of_elements;i++)
{
actual_array[i]=temp_array[i];
}
delete [] temp_array;
temp_array=NULL;
actual_array[number_of_elements]=object;
number_of_elements++;
}
else
{
number_of_elements++;
actual_array = new T[1];
}
}
void Dynamic_Array<T>::operator-=(unsigned int index)
{
T* temp_array = new T[number_of_elements-1];
for(unsigned int i=0, j=0;i<number_of_elements;i++)
{
if(i!=index)
{
temp_array[j]=actual_array[i];
j++;
}
}
delete[] actual_array;
number_of_elements--;
actual_array = new T[number_of_elements];
for(unsigned int i=0;i<number_of_elements;i++)
{
actual_array[i]=temp_array[i];
}
delete [] temp_array;
temp_array = NULL;
}
According to compiler, the error is present in line 18 (the empty one between "};" and "template"
As I said, I have no idea what I screwed up, so any help is appreciated.

Answer 1

When you define member functions outside of a class template declaration then you need to specify the template for each function. When you define
void Dynamic_Array<T>::operator-=(unsigned int index)
{
//...
}
You need to have the template part as well like
template <typename T>
void Dynamic_Array<T>::operator-=(unsigned int index)
{
//...
}
This has to be present for every function definition that you do out of line. A single template <typename T> at the start of all the definition does not apply to all of the function definitions.

Answer 2

Dynamic_Array is a template class so when defining operator+= and operator-= outside the scope of the class you need to provide template type as follows:
template<typename T> void Dynamic_Array<T>::operator+=(T& object) {
//...
}
template<typename T> void Dynamic_Array<T>::operator-=(unsigned int index) {
//...
}
Also, I should note that it is somewhat odd to have void as a return type for operator+= and operator-=, typically you should return a reference to the altered instance of this, i.e:
template<typename T> Dynamic_Array<T>& Dynamic_Array<T>::operator+=(const T& object) {
//...
}