//this program demonstrates two value-returning functions.
//the square function is called in mathematical statement.
#include <iostream>
#include <iomanip>
using namespace std;

//function prototypes
double getRadius();
double square(double);

int main()
{
	const double PI = 3.14159;	//constant for pi
	double radius;				//to hold the circle's radius
	double area;				//to hold the circle's area
	
	//set the numeric output formatting.
	cout << fixed << showpoint << setprecision(2);
	
	//get the radius of the circle.
	cout << "This program calculates the area of ";
	cout << "a circle.\n";
	radius = getRadius();
	
	//calculate the area of the circle.
	area = PI * square(radius);
	
	//display the area.
	cout << "The area is " << area << endl;
	return 0;
}

//******************************************************
// definition of function getRadius.				   *
// this function asks the user to enter the radius of  *
// the circle and then returns that number as a double.*
//******************************************************

double getRadius()
{
	double rad;
	
	cout << "Enter the radius of the circle: ";
	cin >> rad;
	return rad;
}

//******************************************************
// definition of function square.					   *
// this function accepts a double argument and returns *
// the square of the argument s a double.			   *
//******************************************************

double square(double number)
{
	return number * number;
}