How many default constructors per class are possible?

class Birds {};
class Peacock : protected Birds {};

#include<iostream.h> 
int main()
{
    int x = 80; 
    int &y = x;
    x++;
    cout << x << " " << --y;
    return 0;
}

#include<iostream.h> 
class A
{
    public:
    void CuriousTabFunction(void)
    {
        cout<< "Class A" << endl;
    }
};
class B: public A
{
    public:
    void CuriousTabFunction(void)
    {
        cout<< "Class B" << endl;
    } 
};
class C : public B
{
    public:
    void CuriousTabFunction(void)
    {
        cout<< "Class C" << endl;
    } 
};
int main()
{
    A *ptr;
    B objB;
    ptr = &objB;
    ptr = new C();
    ptr->CuriousTabFunction();
    return 0; 
}

#include<iostream.h> 
class TestDrive
{
    int x; 
    public:
    TestDrive(int xx)
    {
        x = xx;
    }
    int DriveIt(void);
};
int TestDrive::DriveIt(void)
{
    static int value = 0;
    int m;
    m = x % 2;
    x = x / 2;
    if((x / 2)) DriveIt(); 
    value = value + m * 10; 
    return value;
}
int main()
{
    TestDrive TD(1234);
    cout<< TD.DriveIt() * 10 << endl;
    return 0; 
}