question about template class

I met a error when running the program. The error is

*** glibc detected *** ./a.out: double free or corruption (fasttop): 0x0000000000c19050 ***

the code is
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#include <cassert>
#include <iostream>

using namespace std;

template<typename T>
class Vector {
	T * data;
	int sz;
public:
	Vector() : data(NULL),sz(0) {
	}
	Vector(int s) {
		data = new T[s]();
		sz = s;
	}
	~Vector() {
		if(data) delete[] data;
	}
	template<typename N> Vector(const Vector<N> & t) {
		int * tmp = new T[sz]();
		for(int i = 0 ; i < sz ; i++) tmp[sz] = t.data[i];
		if(data) delete[] data;
		data = tmp;
	}
	T & operator()(int i) {
		assert(0 <= i && i < sz);
		return data[i];
	}
	template<typename N> Vector<T> & operator=(const Vector<N> & t) {
		int * tmp = new T[sz]();
		for(int i = 0 ; i < sz ; i++) tmp[sz] = t.data[i];
		delete[] data;
		data = tmp;
		return *this;
	}
	template<typename T1,typename T2> friend Vector<T1> f(const Vector<T1> & a,const Vector<T2> & b);
};

template<typename T1,typename T2>
Vector<T1> f(const Vector<T1> & a,const Vector<T2> & b) {
	assert(a.sz == b.sz);
	Vector<T1> retVal(a.sz);
	for(int i = 0 ; i < a.sz ; i++) retVal.data[i] = a.data[i] + b.data[i];
	return retVal;
}

int main()
{
	Vector<int> t1(3),t2(3),t3;
	for(int i = 0 ; i < 3 ; i++) {
		t1(i) = i; t2(i) = i;
	}
	t3 = f(t1,t2);
	return 0;
}

How does the double free happen? Thanks
You need a copy constructor. You do know that if you don't create one, the default will be used, right?
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	Vector(const Vector<T> &t) :
		data(new T[t.sz]),
		sz(t.sz)
	{
		for (int i = 0; i < sz; ++i)
			data[sz] = t.data[i];
	}

He does have one
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	template<typename N> Vector(const Vector<N> & t) {
		int * tmp = new T[sz](); //sz has garbage
		for(int i = 0 ; i < sz ; i++) tmp[sz] = t.data[i];
		if(data) delete[] data; //data has garbage
		data = tmp;
	}
No he doesn't. That isn't a substitute for the correct one.
┬┐So I need to create the specific constructor, that would do the exact same thing as the templatized one? (once the errors are fixed)
Damn.

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		for (int i = 0; i < sz; ++i)
			data[sz] = t.data[i]; //out of bounds 
Yes that copy is incorrect, I missed that.

That templated thing doesn't initialise sz either.
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