Own vector error - c++

Question

I am trying create my own vector, I am at the beginning, and when compile e execute the code, i get "Program not responding". This is the code:
struct X
{
X(){};
~X(){};
int v1, v2, v3;
};
template<typename T>
class Vector
{
public:
// constructors
Vector();
Vector(unsigned s);
virtual ~Vector();
// overloaded operators
T operator[](unsigned index);
// others
void clear();
void add(T value);
unsigned getSize();
bool isEmpty();
private:
// pointer to first item of memory block
T* first;
unsigned size;
};
template<typename T>
Vector<T>::Vector()
{
first = NULL;
size = 0;
}
template<typename T>
Vector<T>::Vector(unsigned s)
{
size = s;
first = new T[s];
};
template<typename T>
Vector<T>::~Vector()
{
clear();
}
template<typename T>
void Vector<T>::clear()
{
for(unsigned i = size ; i > 0 ; i--)
delete &first[i];
first = NULL;
}
template<typename T>
void Vector<T>::add(T value)
{
T* temp = new T[size + 1]; // error happens here
// copy data to new location
for(unsigned i = 0 ; i < size ; i++)
temp[i] = first[i];
// delete older data
clear();
// add the new value in last index
temp[size + 1] = value;
// update the pointer
first = temp;
size++;
}
template<typename T>
T Vector<T>::operator[](unsigned index)
{
return first[index];
}
template<typename T>
unsigned Vector<T>::getSize()
{
return size;
}
template<typename T>
bool Vector<T>::isEmpty()
{
return first == NULL;
}
int main(int argc, char* args[])
{
Vector<X> anything;
X thing;
anything.add(thing);
anything.add(thing);
anything.add(thing); // if remove this line, program work fine.
}
As I commented, error happens in T* temp = new T[size + 1];.
If i define the value of v1, v2, v3 of X class, e.g. X() : v1(0), v2(0), v3(0) { }, the program works correctly.
If i change the type, e.g., Vector of int, he works perfectly.
If put X class in std::vector, work fine too.
Other comments are also accepted.
Can someone helpme?

Answer 1

Your description of the problem is incredibly vague, but I can point out problems with your code:
No vector copy constructor (causes double-deletes and crashes)
No vector copy assignment (causes double-deletes and crashes)
clear is incorrectly calling delete (causes crashes and corruption) (you should match your single new of an array with a single delete of the array. Don't loop over elements.
add is writing past the end of the array (causes crashes and corruption)
add is not exception safe
You have to fix at least the first four. The third and fourth are probably the causes of your hang.

Answer 2

You have a buffer overflow occurring.
T* temp = new T[size + 1]; // When size is 0, you allocate 1 space.
You then assign to the temp array, but in location temp[1], which isn't a valid location because your array has only 1 element. This is undefined behavior, and that this point, your program is free to continue however it chooses. In this case, it seems to loop indefinitely.
// add the new value in last index
temp[size + 1] = value; // When size is zero, your array is length '1', but
// you are accessing temp[1] which is outside the
// bounds of your allocated memory.