How can I build a proper constructor and destructor? - c++

Question

Question #1: How can I build a constructor set the value for (R,PoF,PoR)? I am trying to understand how constructor works but I guess I don't quite get it.
Question #2: Can I build destructor in this way, instead of the way I used in my program?
Circle::~Circle()
{
std::cout << "The fence would cost " << SwimmingPool.PerimeterP(r) << std::endl;
std::cout << "The road would cost " << SwimmingPool.AreaP(r) << std::endl;
std::cout << "Present by FF" << std::endl;
}
I just want the cost to come out by itself, but I don't know how should I create destructor to do so.
Here is my full code:
#include "stdafx.h"
#include "iostream"
const double PI = 3.1415926;
class Circle
{
public:
Circle();
double AreaP(int r);
double PerimeterP(int r);
~Circle();
private:
int R;
int PoF;
int PoR;
};
double Circle::AreaP(int r)
{
return ((r + R)*(r + R) - r*r)*PI*PoR;
}
double Circle::PerimeterP(int r)
{
return (r + R) * 2 * PI*PoF;
}
Circle::Circle()
{
int R = 3;
int PoF = 35;
int PoR = 20;
}
Circle::~Circle()
{
std::cout << "Present by FF" << std::endl;
}
int main()
{
int r;
Circle SwimmingPool;
std::cout << "Please input the radius of the Swimming Pool." << std::endl;
std::cin >> r;
std::cout << "The fence would cost " << SwimmingPool.PerimeterP(r) << std::endl;
std::cout << "The road would cost " << SwimmingPool.AreaP(r) << std::endl;
return 0;
}

Answer 1

You have:
Circle::Circle()
{
int R = 3;
int PoF = 35;
int PoR = 20;
}
That function creates three function local variables and sets their values. It does not initialize the members of the class. Change it to:
Circle::Circle() : R(30), PoF(35), PoR(20) {}
Always prefer to initialize in the initializer list instead of setting the values in the body of the constructor.
No, you may not use:
Circle::~Circle()
{
std::cout << "The fence would cost " << SwimmingPool.PerimeterP(r) << std::endl;
std::cout << "The road would cost " << SwimmingPool.AreaP(r) << std::endl;
std::cout << "Present by FF" << std::endl;
}
SwimmingPool is a variable in main. It cannot be used in the destructor. Besides, it does not make sense to print those messages in the destructor. It should simply be
Circle::~Circle()
{
}

Answer 2

Circle::Circle() : R(3), PoF(3), PoR(3) {};
Define the R, PoF, PoR as const int
The destructor must not throw an exception and generally you want it to release resources acquired by the object. Usually not the best place to be outputting stuff to stdout.
Don't use std::endl unless you want to flush the stream. Use '\n' instead.