C# triangle area

double traingleArea  = base * height / 2; 

import java.util.Scanner;

public class shw2point15 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.println("Enter three points for a triangle:");

        double x1 = input.nextDouble();
        double y1 = input.nextDouble();
        double x2 = input.nextDouble();
        double y2 = input.nextDouble();
        double x3 = input.nextDouble();
        double y3 = input.nextDouble();


        double s = ((x1 + y1) + (x2 + y2) + (x3 + y3)) / 2;
        double area = Math.sqrt(s * (s - (x1 - y1)) * (s - (x2 - y2)) * (s - (x3 - y3)));



        System.out.println("The area of the triangle is " + area);
    }
}

 namespace TriangleCalc; 
 public class Program
 {
     private double A { get; set; }
     private double B { get; set; }
     private double C { get; set; }
     public void Triangle()
     {
         try
         {
             this.A = Convert.ToDouble(Console.ReadLine());
             Console.WriteLine("a is " + A);
             this.B = Convert.ToDouble(Console.ReadLine());
             Console.WriteLine("b is " + B);
             this.C = Convert.ToDouble(Console.ReadLine());
             Console.WriteLine("c is " + C);
         }  catch
         {
             throw (new Exception("Triangle's side must be a number"));
         }
     }
     
     public void Area()
     {
             if (A + B > C && B + C > A && A + C >B )  
             {
                 var s  = (A+B+C)/2;
                 var result = Math.Sqrt(s * (s - A) * (s - B) * (s - C));
                 Console.WriteLine("The area is " + result );
             }
             else
             {
                 Console.WriteLine("Result is NaN");
             }
     }
     
     public void Perimeter()
     {
         if (A + B > C && A + C > B && B + C > A)
         {
             var perimeter = A + B + C;
             Console.WriteLine("The perimeter is " + perimeter);
         }
         else
         {
             Console.WriteLine("Such triangle doesn't exist");
         }
     } 
 }

public class Runner : Program
{
    public static void Main(string[] args)
    {
        while (true)
        {
            Console.WriteLine("1-Start\n2-Stop");
            var input1 = Convert.ToInt32(Console.ReadLine());

            if (input1 == 1)
            {
                var startProgram = Triangleİtems.Start;
            }
            else
            {
                throw (new Exception("Program must start with 1"));
            }

            var triangle = new Program();
            triangle.Triangle();
            triangle.Area();
            triangle.Perimeter();

            Console.WriteLine("You can end program with 2");
            input1 = Convert.ToInt32(Console.ReadLine());

            if (input1 == 2)
            {
                var stopProgram = Triangleİtems.Stop;
            }

            else
            {
                throw (new Exception("Program must stop with 2"));
            }
        }
    }
}

public static class Triangleİtems
{
    public static DateTime Start;
    public static DateTime Stop;

    public static DateTime StartProgram()
    {
        Start = DateTime.Now;
        return Start;
    }

    public static DateTime StopProgram()
    {
        Stop = DateTime.Now;
        return Stop;
    }
}

import java.util.Scanner;
class AreaOfTriangle3 
{
   public static void main(String args[]) 
    {   
       
      Scanner s1= new Scanner(System.in);
        
         System.out.println("Enter the 1st side:");
         int a= s1.nextInt();
 
         System.out.println("Enter the 2nd side:");
          int b= s1.nextInt();
 
         System.out.println("Enter the 3rd side:");
         int c= s1.nextInt();
        if((a+b)>c && (a+c)>b && (b+c)>a)
          {
            int s=(a+b+c)/2;
            double  area=Math.sqrt(s*(s-a)*(s-b)*(s-c));
             System.out.println("Area of Triangle is: " + area);    
           }
         else  
           System.out.println("Area of Triangle not exit");
   }
}