Help! I need code explanation

[JetJaguar]

Hello, guys!! I have to answer what will the variable values be in the following code, but I do not understand it.

   #include<iostream>
using namespace std;
class TstA{
  static int c;
  double d; int n;
public:
  TstA(int x=1):d(x*2.){n=c--;}
  TstA(TstA & t){
     d=t.d;n=t.n*10-c--;
  }
  ~TstA(){
     cout<<"End#"<<n<<endl; c++;
  }
  void show(){
     cout<<"Tst#"<<n<<": "<<d<<endl;
  }
  static int status(){
     return c;
  }
};

int TstA::c=0;
void f(TstA t){t.show();}

int main(){
  TstA  b[2];
  {TstA a(5), c=a;
   cout<<c.status()<<endl;
   for(int i=0;i<2;i++)b[i].show();
   f(c);
  }
  cout<<TstA::status()<<endl;
}

[DonRumata]

So, every object of class TstA has two fields - d and n. Besides class TstA contains static field that set with initial value = 0 and decrements when new object is created and increments when one of current objects is destroyed.

 TstA  b[2]; // creates two objects with defalult constructor
// c = 0, so for first one d = 2.0, n = 0, c becomes -1
// c = -1, so for second one d = 2.0, n = -1, c becomes -2
TstA a(5); // creates one more object with default constructor but with user-defined value
// instead of default. c = -2, so for this one d = 10.0, n = -2, c becomes -3
TstA = c; // creates last object with copy constuctor.
// c = -3, so d = 10.0 and n  = -17, c becomes -4;
 for(int i=0;i<2;i++)b[i].show();
 f(c);
// this lines prints values described before
// Then we leave separated scope {} and all static objects will be removed with their //destructors so we getting next cout messages and c is incremented twice.
//-4 + 2 = -2
//So c = -2 and last cout proves it.
 cout<<TstA::status()<<endl;

UPD: Ooops, my bad about undeclared c, i just some reformated code for better readability and got an error.

[dhayden]

Here is the code with indenting and some output in the constructors and destructor.

#include<iostream>

using namespace std;

class TstA
{
    static int c;
    double d;
    int n;
public:
    TstA(int x = 1):d(x * 2.) {
	cout << "TstA(" << x << ") c=" << c << " this=" << this << '\n';
	n = c--;
    }
    TstA(TstA & t)
    {
	cout << "TstA(" << &t << ") c=" << c << " this=" << this << '\n';
	d = t.d;
	n = t.n * 10 - c--;
    }
    ~TstA() {
	cout << "destroy " << this << endl;
	c++;
    }
    void show()
    {
	cout << "Tst#" << n << ": " << d << endl;
    }
    static int status()
    {
	return c;
    }
};

int TstA::c = 0;

void
f(TstA t)
{
    t.show();
}

int
main()
{
    TstA b[2];
    {
	TstA a(5), c = a;
	cout << c.status() << endl;
	for (int i = 0; i < 2; i++)
	    b[i].show();
	f(c);
    }
    cout << TstA::status() << endl;
}

And here is the output. Note that the values for "this" will be different on your system, just use them to see what object is getting passed around where.

TstA(1) c=0 this=0xffffcbb0
TstA(1) c=-1 this=0xffffcbc0
TstA(5) c=-2 this=0xffffcba0
TstA(0xffffcba0) c=-3 this=0xffffcb90
-4
Tst#0: 2
Tst#-1: 2
TstA(0xffffcb90) c=-4 this=0xffffcbd0
Tst#-166: 10
destroy 0xffffcbd0
destroy 0xffffcb90
destroy 0xffffcba0
-2
destroy 0xffffcbc0
destroy 0xffffcbb0

Some comments in addition to DonRumata's (using my line numbers):
Line 38: notice that t is passed by value. That means the copy constructor gets called, and the destructor gets called when f() exits.
Line 53: TstA objects a and c created at line 48 get destroyed here.