C#

using System;

namespace areaOfFigures
{
    class Program
    {
        static void Main(string[] args)
        {


            var figureName = Console.ReadLine();
            var sum = 1.00;

            switch (figureName)
            {
                case "square":
                    var a = double.Parse(Console.ReadLine());
                    sum = a * a;
                    Console.WriteLine("{0:F3}",sum);
                    break;

                case "rectangle":
                    var widgt = double.Parse(Console.ReadLine());
                    var height = double.Parse(Console.ReadLine());
                    sum = widgt * height;
                    Console.WriteLine("{0:F3}",sum);
                    break;

                case "circle":
                    var r = double.Parse(Console.ReadLine());
                    sum = Math.PI * (r * r);
                    Console.WriteLine("{0:F3}", sum);
                    break;

                case "triangle":
                    var h = double.Parse(Console.ReadLine());
                    var side = double.Parse(Console.ReadLine());
                    sum = (side * h) / 2;
                    Console.WriteLine("{0:F3}", sum);
                    break;
            }






        }
    }
}