Revise paste triangle 14.11.20205

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace _00.Demo
{
    internal class Triangle
    {
        private double _a;
        private double _b;
        private double _c;

private void ValidateSide(double value, string sideName)
        {
            if (value <= 0)
            {
                throw new ArgumentException($"The side {sideName} has to be more than zero");
            }
        }
        public double A
        {
            get
            {
                return this._a;
            }
            private set
            {
                ValidateSide(value, nameof(A));
                this._a = value;
            }
        }
        public double B
        {
            get
            {
                return this._b;
            }
            private set
            {
                ValidateSide(value, nameof(B));
                this._b = value;
            }
        }
        public double C
        {
            get
            {
                return this._c;
            }
            private set
            {
                ValidateSide(value, nameof(A));
                this._c = value;
            }
        }

public Triangle(double a, double b, double c)
        {
            if (a + c <= b ||
                b + c <= a ||
                a + b <= c)
            {
                throw new ArgumentException("The triangle does not exist");
            }

this.A = a;
            this.B = b;
            this.C = c;
        }

public double P()
        {
            return this.A + this.B + this.C;
        }
        public double S()
        {
            double p = P() / 2;
            double S = Math.Sqrt(p * (p - this.A) * (p - this.B) * (p - this.C));
            return S;
        }

}
}