Circle Class Problem

I am having trouble understanding classes and this is the first problem I have to do. If I could get some help with it I will be able to do the rest of my homework.

Write a Circle class that has the following member variables:
radius: a double
pi: a double initialized with the value 3.14159

The class should have the following member functions:
Default Constructor. A default constructor that sets the radius to 0.0
Constructor. Accepts the radius of the circle as an argument
setRadius. A mutator function for the radius variable
getRadius. An accessor function for the radius variable
getArea. Returns the area of the circle, which is calculated as diameter=pi*radius*radius
getDiameter. Returns the diameter of the circle, which is calculated as diameter=radius*2
getCircumference. Returns the circumference of the circle, which is calculated as circumference=2*pi*radius

Write a program that demonstrates the Circle class by asking the user for the circle's radius, creating a circle object, and then reporting the circle's area, diameter, and circumference.
I suggest you read over this carefully. It goes over everything you listed.

If you have started to write the code and are still stuck, feel free to post what you have and we can help from there.
Why would pi be a member variable? For one thing, it is a constant. For another, each individual circle doesn't need its own separate value of pi.

But still, that doesn't help you. I'm just puzzled by the design.
LOL I have no clue that is just the way the question is worded!
This is what I have so far. All the program does is ask for radius then closes

#include <cstdlib>
#include <iostream>

using namespace std;

#include <iostream.h>
#include <math.h>

const double PI = 3.14159;

// class interface (definition)
class Circle
// constructors
Circle(); // default constructor
Circle(const Circle &); // copy constructor

// member functions (methods)
void SetRadius(double); // modifier that sets new radius
double Area();

// member variables (data)
double radius; // circle's radius

int main()
Circle myCircle; // circle object used as an example
double circleArea = 0.0; // area of the circle
double userInput = 0.0; // user input for radius of circle

cout << "Enter radius of the circle: ";
cin >> userInput;

circleArea = myCircle.Area();

cout << "The area is " << circleArea << endl << endl;

return 0;
}// end of main

// class implementation

// default constructor
radius = 0.0;

// copy constructor
Circle::Circle(const Circle & Object)
radius = Object.radius;

// sets the radius of the circle
void Circle::SetRadius(double IncomingRadius)
radius = IncomingRadius;

// computes the area of the circle
double Circle::Area()
return(PI * pow(radius, 2));
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