Question: Do we have to explicitly define a default constructor when we define a copy constructor for a class?? Please give reasons.

eg: 

```
class A 
{
    int i;

    public:
           A(A& a)
           {
               i = a.i; //Ok this is corrected....
           }

           A() { } //Is this required if we write the above copy constructor??
};      

```

Also, if we define any other parameterized constructor for a class other than the copy constructor, do we also have to define the default constructor?? Consider the above code without the copy constructor and replace it with 

```
A(int z)
{
    z.i = 10;
}

```

Alrite....After seeing the answers I wrote the following program.

```
#include <iostream>

using namespace std;

class X
{
    int i;

    public:
            //X();
            X(int ii);
            void print();
};

//X::X() { }

X::X(int ii)
{
    i = ii;
}

void X::print()
{
    cout<<"i = "<<i<<endl;
}

int main(void)
{
    X x(10);
  //X x1;
    x.print();
  //x1.print();
}

```

ANd this program seems to be working fine without the default constructor. Please explain why is this the case?? I am really confused with the concept.....

Answer: 
You don't have to define both. However, once you define any constructors for a class, all the default ones become unavailable. So - if you want to both copy-construct and to construct without copying, you need to define an non-default (ie explicit) default (ie no parameters) constructor too.

If you define a copy constructor, you should normally override the assignment operator too.
1) Constructor with no argument is called 'default Constructor'.
2) If user have not provided any of the following constructor, then the compiler declares
 the default constructor for you. 

```
  2a) Copy Constructor
  2b) Non-default constructor
  2C) default constructor. 

```

3) If compilers declares the 'default constructor', then it is said to be 'implicitly declared default constructor', 

4) The 'implicitly declared default constructor' are of two types 

```
   4a) **trivial** Constructor
   4b) **non-trivial** Constructor. 

```

5) Implictly declared default constructor is said to be 'trivial', when there is 
 5a) No reference variable 
 5b) No Virtual Function
 5c) No Virtual Base Class.
 5d) Parent class has 'trivial' constructor, 

```
Else, it is said to be 'non-trivial'.

```

Hope this helps.