Function Practice
------------------

Problem 1: Write a program that takes a radius as input and calculates the diameter, the circumference and area of the given circle using functions

double Diameter(double radius);
double Circumference(double radius);
double Area(double radius);
 

const int PI = 3.14159;

int main()
{
	double radius;

	cout << "Please enter the radius of a circle: ";
	cin >> radius;

	cout << "The diameter of the circle is: " << Diameter(radius) << endl;
	cout << "The circumference of the circle is: " << Circumference(radius) << endl;
	cout << "The area of the circle is: " << Area(radius) << endl;
}

double Diameter(double radius) 
{
    return (2 * radius);
}
 
double Circumference(double radius) 
{
    return (2 * M_PI * radius); 
}

double Area(double radius)
{
    return (M_PI * radius * radius); 
}


Problem 2: Write a function that gets an integer from the user. Do all appropriate error checking.

int GetIntegerFromUser()
{
	bool failure;
	int number;
	do
	{
		failure = false;
		cout << "Please enter an integer: ";
		cin >> number;

		if (cin.fail())
		{
			cin.clear();
			cin.ignore()
			cout << "Input error! Please try again."<<endl;
			failure = false;
		}

	}while(failure);
	
	return number;
}