Compute Area and Circumference of Circle.

[rayjeyz]

// ProgrammingAssignmentSeven.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <cmath>

using namespace std;

const double  PI = 3.14;
//  ===================
//  Function Prototypes
//  ===================
    void Banner();
	void Getvalue(double&);
	double computeCircumference(double);
	void computeArea(double&, double );
//  ===============
    int main() { 
		double c;
		double  radius = 0;
		double area = 0;
		double a;
		Banner();
		

		Getvalue(radius);
	
		c = computeCircumference(radius);
		 a = computeArea(radius,area);

       cout << c << endl;
	   cout << a << endl;
	    return 0;

    } // Function Main
//  ==================

//  ==================
	void Banner() {
		cout << "================================================" << endl;
		cout << "Welcome to my Programming Assignment Seven.  "     << endl;
		cout << endl;
		cout << "Please Enter a value for the radius of a circle." << endl;
		cout << "I will tell the circumference and area of it. "   << endl;
		cout << "================================================" << endl;
		cout << endl;

	} // Function Banner
//  ===================

//  ==================
	void Getvalue(double& radius2) {
	
	cout << "Please enter your radius of a circle: ";
	cin >> radius2;

	
	} // Funciton Getvalue
//  ======================

//  ====================
    double computeCircumference( double radius1) {

		double c;

		c = 2*PI*radius1;

		return c;
	}// Function computecircumference
//  =================================

//  ================
	void computeArea(double radius2, double& a) {

		

		a = PI*pow(radius2,2);
		
		
	}

cannot convert from 'void' to 'double' This happens at the line 30.
The program does compute the Circumference, and I am trying to compute the Area, but it doesn't work. Please help me ^_^
Thank you.

[Zhuge]

computeArea does not return anything, but you are trying to get a return value from it on line 30.