why this value -858993460?

This is my code:

// cl2.h
class cl2{
 int numero;
  public:
  int Aggiungi()
    {
		 return numero;
    }
 };

 //main.cpp
#include <iostream>
#include "cl2.h"
using namespace std;
int main(...)
{
        int j ;
	cl2 c ;
	j = c.Aggiungi();
	cout << j << endl;
	return 0;
}

I see on the screen always the value  -858993460.
Is there a reason for these.
I already know that I can fix the problem with contructors, but here I
just want to understand why.

     Giuseppe