Simple Vector problem

[Sam99]

#include <iostream>
using namespace std;

int size = 10;

template <class T> class vector {
    T* v;
  public:
	  vector()
	  {
		  v = new T[size];
	  }

	  vector(T* a)
	  {
		  v = new T[size];
		  for (int i=0; i<size;i++)
			  v[i]=a[i];
	  }

	  friend ostream &operator << (ostream &o, vector t)
	  {
		  for(int i=0; i<size; i++)
			  o<<t.v[i]<<endl;
		  return o;
	  }
};


int main()
{
	int x[10] = {1,2,3,4,5,6,7,8,9,10};

	vector <int> v1;
	v1=x;

	cout<<v1;

	system ("Pause");
	return 0;
}

At the very beginning, in global area, I initialized size=10.
But if I want to put this in my parameterized constructor, it shows error. Why?

[Sam99]

Instead of initialize in global area, I want to initialize the size in private, and then set its default value if default constructor vector(). But it shows an error. Why?

vector()
	  {
                  size=10;
		  v = new T[size];
	  }

[mutexe]

because you use that variable in a few others places that are outside the scope of your first constructor?