#include <iostream>
#include <iomanip>
using namespace std;

// function prototypes
void errorRadius();
void errorRectangle();
void errorTriangle();
void showMenu();
double getRadius();
void successfulTerminationOfProgramMessage();
void errorInvalidMenuOption();
double areaCircle(double);
double areaRectangle(double, double);
double areaTriangle( double, double);
bool validRadius(double);
bool validLengthAndWidth(double, double);
bool validBaseAndHeight(double, double);

// My Geometry Calculator

int main()
{
int selection;
double radius, length, width, base, height;

do{
// display the Geometry Calculator menu
showMenu();
cin>>selection; // Get the user's selection
cout<<fixed <<showpoint <<setprecision(4);

switch (selection)
{
    case 1: cout<<"\n\t\t~~~~~~~~~~~~~~~~~~~~~~~~~~~\n";
    cout<<"\t\t\tArea of a Circle\n\n";
    radius = getRadius(); // Get the radius
    areaCircle(radius); // call acreaCircle function, and multiply PI to get area

    // if user gives negative radius display error message, if not then display the circle's radius
    if (validRadius(radius))
    {
        errorRadius();
    }
    else
    {
        cout<<"\t\tArea = " <<areaCircle(radius) <<" square units\n";
    }
        cout<<"\n\t\t~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\n";
        break;


    case 2: cout<<"\n\t\t~~~~~~~~~~~~~~~~~~~~~~~~~~~\n";
    cout<<"\t\t\tArea of a Rectangle\n\n";
    cout<<"\t\tEnter length: ";
    cin>>length; // get length
    cout<<"\t\tEnter width: ";
    cin>>width; // get width
    areaRectangle(length, width); // call areaRectangle function
    // if the length or width is negative display error message, if not then display the rectangles's area
    if (validLengthAndWidth(length, width))

    {
        errorRectangle();
    }
    else
    {
       cout<<"\t\tArea = " <<areaRectangle(length, width) <<endl;
    }
        cout<<"\n\t\t~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\n";
        break;


    case 3: cout<<"\n\t\t~~~~~~~~~~~~~~~~~~~~~~~~~~~\n";
    cout<<"\t\t\tArea of a Triagnle\n\n";
    cout<<"\t\tEnter length of base: ";
    cin>>base; // get base
    cout<<"\t\tEnter height: ";
    cin>>height; // get height
    areaTriangle(base, height);
    // if the base or height is negative display error message, if not then display the triangle's area
    if (validBaseAndHeight(base, height))
    {
        errorTriangle();
    }
    else
    {
        cout<<"\t\tArea = " <<areaTriangle(base, height) <<endl;
    }
    cout<<"\n\t\t~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\n";
    break;

    case 4: successfulTerminationOfProgramMessage(); // exit the program
    break;

    // display error message if user selects an invalid number
    default: errorInvalidMenuOption();
}
}while(selection != 4);

 return 0;
}

// function definitions

void errorRadius()
{
    cout<<"\n\t\t**Error: Radius cannot be negative" <<endl;
}

void errorRectangle()
{
    cout<<"\n\t\t**Error: Length and width must be a positive value" <<endl;
}

void errorTriangle()
{
    cout<<"\n\t\t**Error: Base and height must be a positive value" <<endl;
}

void showMenu()
{
cout<<"\t\t\tGeometry Calculator" <<endl <<endl;
cout<<"\t\t1. Calculate the Area of a Circle" <<endl;
cout<<"\t\t2. Calculate the Area of a Rectangle" <<endl;
cout<<"\t\t3. Calculate the Area of a Triangle" <<endl;
cout<<"\t\t4. Quit" <<endl <<endl;
cout<<"\t\tEnter your choice (1-4): ";
}

double getRadius()
{
    double rad;

    cout<<"\n\t\tEnter radius of the circle: ";
    cin>>rad;
    return rad;
}

void successfulTerminationOfProgramMessage()
{
    cout<<"\n\t\tThank you for using the Geometry Calculator\n";

}

void errorInvalidMenuOption()
{
    cout<<"\n\t\t**Error: Menu option must be 1, 2, 3, or 4\n";
    cout<<"\n\t\t~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\n";
}

double areaCircle(double num1)
{
    const double PI = 3.14159;
    double result;
    result = (num1 * num1) * PI;
    return result;
}

double areaRectangle(double num2, double num3)
{
    double product;
    product = num2 * num3;
    return product;
}

double areaTriangle(double number1, double number2)
{
    double product;
    product = (number1 * number2) * 0.5;
    return product;
}

bool validRadius(double number)
{
    bool status;
    if(number < 0)
        status = true;
    else
        status = false;
    return status;
}

bool validLengthAndWidth(double number1, double number2)
{    bool status;
    if (number1 < 0 || number2 < 0)
        status = true;
    else
        status = false;
    return status;
}

bool validBaseAndHeight(double a, double b)
{
    bool status;
    if (a < 0 || b < 0)
        status = true;
    else
        status = false;
    return 0;
}