LNK error, unresolved external...

Ok, first problem taken care of, but why these errors? They go away if I inline the functions in the header file. Thanks for any help.
Header file

Code:

#include <iostream>
using namespace std;
template <class T>
class Array  
{
public:
	Array(int = 10);
	virtual ~Array() {delete [] ptr;}
	T &operator[](int);
	int getSize() const {return size;}

private:
	T *ptr;
	int size;
};

Implementation

Code:

#include <iostream>
#include <cassert>

using namespace std;

#include "t_Array.h"

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////

template<class T>
Array<T>::Array(int arraySize)
{
	size = (arraySize > 1 ? arraySize : 10);
	ptr = new T[size] = {0};
	assert(ptr != 0);
	cout << "This is the class template version" << endl;
}

template<class T>
T &Array<T>::operator[](int subscript)
{
	assert(1 <= subscript && subscript < size);
	return ptr[subscript];
}

Driver

Code:

#include <iostream>
using namespace std;
#include "t_Array.h"

int main()
{
	Array<double> tArray(15);

	for (int i = 0; i < tArray.getSize(); i ++)
	{
		tArray[i] = i + 0.5;
		cout << tArray[i] << endl;
	}
	return 0;
}

Errors

Code:

Compiling...
t_Array.cpp
Linking...
TempArray.obj : error LNK2001: unresolved external symbol "public: double & __thiscall Array<double>::operator[](int)" (??A?$Array@N@@QAEAANH@Z)
TempArray.obj : error LNK2001: unresolved external symbol "public: __thiscall Array<double>::Array<double>(int)" (??0?$Array@N@@QAE@H@Z)
Debug/TempArray.exe : fatal error LNK1120: 2 unresolved externals
Error executing link.exe.

TempArray.exe - 3 error(s), 0 warning(s)

MSVC and templates don't mix well. Put the definitions and declarations in the same file and the problems should disappear.

Ok, that works, no idea why it didn't the other way though. Thanks.
Now, though, how do I declare a default initialization for the constructor? I'm trying to allow an Array to be declared as Array <int> iArray(15); which works fine, or as Array<int> iArray(); with no parameter passed. This doesn't work. The working constructor is below. I tried overloading it with a version that took no arguments, but that didn't work either. Normally the header file would have a default initialization passed to the constructor definition in the implementation file, but I got rid of that file to get the program to compile. How can I get Array<int> iArray(); (or float, double, etc) versions to work? Thanks.

Code:

template <class T>
class Array  
{
public:
	Array(int arraySize)
	{
		size = (arraySize > 1 ? arraySize : 10);	// Check & set valid array size
		ptr = new T[size];	// Allocate memory for array 
		assert(ptr != 0);	// Check if memory allocated
		for (int i = 0; i < size; i++)
			ptr[i] = 0;
		cout << "This is the class template version of the ";
	}

Just put a default argument in -

Code:

Array(int arraySize=10)
	{
		size = (arraySize > 1 ? arraySize : 10);	// Check & set valid array size
		ptr = new T[size];	// Allocate memory for array 
		assert(ptr != 0);	// Check if memory allocated
		for (int i = 0; i < size; i++)
			ptr[i] = 0;
		cout << "This is the class template version of the ";
	}

But in your driver make sure you create an instance like -

Array<int> tArray;

rather than

Array<int> tArray();