#include <iostream>
#include <cmath>


using namespace std;



int GetNonNegativeInteger ()
{
     int input;
     cin >> input;
     while (input < 0)
     {
          // display error message.
          // ask for input again
     }

     return input;
}



int main ()

{
		double const pi=3.14159;
		int radius,
			length,
			width,
			base,
			height,
			choice;
		double	area;
		
		

	//Display the menu and get the user's choice
		cout << "         Geometry Calculator \n\n";
		cout << "1. Calculate the Area of a Circle\n";
		cout << "2. Calculate the Area of a Rectangle\n";
		cout << "3. Calculate the Area of a Trainge\n";
		cout << "4. Quit\n";
		cout << "\n";

		cout <<"Enter your choice (1-4): ";
		cin >> choice;
		cout << "\n";

		if (choice==1)
		   {cout << "Please enter the radius of the circle: ";
			radius = GetNonNegativeInteger ();
			area = radius * pi;
			cout << "The area of the circle is: " << area << endl;}

		   else if (choice==2)
		   {cout << "Please enter the length of the rectangle: ";
			length = GetNonNegativeInteger ();
			cout << "Please enter the width of the rectangle: ";
			width = GetNonNegativeInteger ();
			area = length * width;
			cout << "The area of the rectangle is: " << area << endl;}
     
			else if (choice==3)
			{cout << "Please enter the base length of the triangle: ";
			cin >> base;
			cout << "Please enter the height of the triangle: ";
			cin >> height;
			area = (base * height)/2;
			cout << "The area of the triangle is: " << area << endl;}
     
			else if (choice==4)
			{cout << "Thanks for trying the Geometry Calculator\n";}

			else
			{cout << "You can only select options 1-4, run the program again and select a option 1-4\n"; }
     
     
		return 0;

}