Copy constructor

[ak3000]

I'm confused how each object calls the member function. can anyone give me step by step working of this code

#include <iostream>

using namespace std;

class add 
{
	int num1, num2, sum;
	public:
	add()
	{
		 cout<<" constructor without parameters ";
		 num1 = '\0';
		 num2='\0';
		 sum='\0';
		 
	}
	add(int s1, int s2)
	{
		cout<<"\n constructor with parameters";
		num1= s1;
		num2= s2;
		sum= '\0';
		
	}
	add(add &a)
	{
		cout<<"\ncopy const";
		num1= a.num1;
		num2 = a.num2;
		sum= '\0';
		
	}
	
	void getdata()
	{
		cout<<"\nenter data";
		cin>>num1>>num2;
		
	}
	void addition(add b)
	{
		sum = num1+num2+ b.num1 + b.num2 ;
	
	}
	add addition()
	{
		add a(5,6);
		sum = num1+ num2 + a.num1 + a.num2;
		
	}
	void putdata()
	{
		cout<<"\nthe  numbers are";
		cout<<num1<<'\t'<< num2 ;
		cout<< "\nthe sum of the numbers are"<<sum;
		
	}
};

int main()
{
	add a,b(10,20), c(b);
	a.getdata();
	a.addition();
	b=c.addition();
	c.addition();
	cout<<"\nobj a";
	a.putdata();
	cout<<"\n obj b ";
	b.putdata();
	cout<<"\n obj c ";  
	c.putdata();
	
}

p.s the output of this program is absurd but its main motive is to understand where the copy constructor has been invoked.
also can you explain what is being done in this function block

add(add &a)
	{
		cout<<"\ncopy const";
		num1= a.num1;
		num2 = a.num2;
		sum= '\0';
		
	}

thanks in advance.

[2kaud]

Firstly, this code doesn't compile.

add addition()
	{
		add a(5,6);
		sum = num1+ num2 + a.num1 + a.num2;
	}

This function returns a type of add, but it doesn't have a return statement. Consider

add addition()
	{
		add a(5,6);
		sum = num1+ num2 + a.num1 + a.num2;
                return *this;		
	}

The point of a copy constructor is to produce a new class instance that has the same contents as the original. So

add(add &a)
	{
		cout<<"\ncopy const";
		num1= a.num1;
		num2 = a.num2;
		sum= '\0';
	}

produces a copy that isn't a copy as sum is 0. Consider

add(const add &a)
	{
		cout<<"\ncopy const";
		num1= a.num1;
		num2 = a.num2;
		sum= a.sum;
	}

also the copy constructor usually has a const parameter so that a non-modifiable argument can be passed.

can anyone give me step by step working of this code

A constructor creates a new instance of a class and should initialise all non-static class variables. A copy constructor creates a new class instance as a copy of an existing class instance (note issues with using dynamic memory here - but that's a different question). A copy constructor is automatically called when a copy of a class instance is required - such as passing a class instance by value as a function parameter.

The best way to understand code and to determine how it works is to use the debugger to step through the code line by line. If you do this and then still have specific questions, we'll be able to provide more guidance.