using System;

​

public class Program

{

    public static void Main()

    {

        for (int externalLoop = 0; externalLoop < 1;  externalLoop++)

        {

        //gathering which shape they want they area of 

        Console.WriteLine("1) Area of a Square\n\n2) Area of a Rectangle\n\n3) Area of Triangle\n\nWhich shape would you like to find the area of? (enter 1, 2, or 3): ");

        string answer = Console.ReadLine().ToLower();

        if (answer == "1" || answer == "square" || answer == "s") //if they want the area of a square

        {

            for (int sideLoop = 0; sideLoop < 1; sideLoop++)

            {

                //gathering the the length of the sides

                Console.Clear();

                Console.Write("What is the length of the side?: ");

                double side;

                bool sideTest = double.TryParse(Console.ReadLine(), out side);

                Console.Clear();

                if (sideTest == true)

                {

                    //writing out the area

                    Console.WriteLine("The area of the square is " + Area(side));

                    Console.WriteLine("\nWould you like to go again? (Enter yes or no): ");

                    string rego = Console.ReadLine().ToLower();

                    if (rego == "yes" || rego == "y" || rego == "ye") externalLoop -= 1;

                    else externalLoop = 1;

                }

                else if (sideTest == false)

                {

                    //error message

                    Console.WriteLine("Please enter your input as a number\n");

                    sideLoop -= 1;

                }

            }

        }

        if (answer == "2" || answer == "rectangle" || answer == "r") //if they want the area of a rectagle

        {

            for (int lengthLoop = 0; lengthLoop < 1; lengthLoop++)

            {

                //gathering the length of the rectangle

                Console.Clear();

                Console.Write("What is the length of the rectangle?: ");

                double length;

                bool lengthTest = double.TryParse(Console.ReadLine(), out length);

                Console.Clear();

                if (lengthTest == true)

                {

                    for (int widthLoop = 0; widthLoop < 1; widthLoop++)

                    {

                        //gathering the width of the rectangle

                        Console.Write("What is the width of the rectangle?: ");

                        double width;

                        bool widthTest = double.TryParse(Console.ReadLine(), out width);

                        Console.Clear();

                        if (widthTest == true)

                        { 

                            //writing out the are of the rectangle

                            Console.WriteLine("The area of the rectangle is " + Area(length, width));

                            Console.WriteLine("\nWould you like to go again? (Enter yes or no): ");

                            string rego = Console.ReadLine().ToLower();

                            if (rego == "yes" || rego == "y" || rego == "ye") externalLoop -= 1;

                        }

                        else if (widthTest == false)

                        {

                            //error message

                            Console.WriteLine("Enter your width as a nubmer.\n");

                            widthLoop -= 1;

                        }

                    }

                }

                else if (lengthTest == false)

                {

                    Console.WriteLine("Please enter your input as a number.\n");

                    lengthLoop -= 1;

                }

            }

        }   

        if (answer == "3" || answer == "triangle" || answer == "t")

        {

            for (int side1Loop = 0; side1Loop < 1; side1Loop++)

            {

                Console.Clear();

                Console.Write("What is the first side of the triangle?: ");

                double side1;

                bool side1Test = double.TryParse(Console.ReadLine(), out side1);

                Console.Clear();

                if (side1Test == true)

                {

                    for (int side2Loop = 0; side1Loop < 1; side1Loop++)

                    {

                        Console.Write("What is the second side of the triangle?: ");

                        double side2;

                        bool side2Test = double.TryParse(Console.ReadLine(), out side2);

                        Console.Clear();

                        if (side2Test == true)

                        {

                            for (int side3Loop = 0; side3Loop < 1; side3Loop++)

                            {

                                Console.Write("What is the third side of the triangle?: ");

                                double side3;

                                bool side3Test = double.TryParse(Console.ReadLine(), out side3);

                                Console.Clear();

                                if (side3Test == true)

                                {

                                    Console.WriteLine("The area of the triangle is " + Area(side1, side2, side3));

                                    Console.WriteLine("\nWould you like to go again? (Enter yes or no): ");

                                    string rego = Console.ReadLine().ToLower();

                                    if (rego == "yes" || rego == "y" || rego == "ye") externalLoop -= 1;

                                }

                                else if (side3Test == false)

                                {

                                    Console.WriteLine("Please enter your third side as a number.\n");

                                    side3Loop -= 1;

                                }

                            }

                        }

                        else if (side2Test == false)

                        {

                            Console.WriteLine("Please enter your second side as a number.\n");

                            side2Loop -= 1;

                        }

                    }

                }

                else if (side1Test == false)

                {

                    Console.WriteLine("Please enter your first side as a number\n");

                    side1Loop -= 1;

                }

            }

        }

        else if ( answer != "1" || answer != "square" || answer != "s" ||  answer != "2" || answer != "rectangle" || answer != "r" || answer != "3" || answer != "triangle" || answer != "t")

        {

            Console.Clear();

            Console.WriteLine("Enter one of the given options\n");

            externalLoop -= 1;

        }

        }

        Console.Clear();

    }

​

    //area of a square

    private static double Area(double side)

    {

        return side * side;

    }

​

    //area of a rectangle

    private static double Area(double length, double width)

    {

        return length * width;

    }

​

    //area of a triangle

    private static double Area(double a, double b, double c)

    {

        double s = (a + b + c) / 2;

        double under = s * ( s - a ) * ( s - b ) * ( s - c);

        double final = Math.Sqrt(under);

        return final;

    }

}