using System;

using System.Collections.Generic;

public class Program

{

    internal class Value

    {

        public Value(decimal? gross, decimal? net, bool expected)

        {

            Gross = gross;

            Net = net;

            ExpectedValidationResult = expected;

        }

        public decimal? Gross {get; set;}

        public decimal? Net {get; set;}

        public bool ExpectedValidationResult {get; set;}

​

        public override string ToString()

        {

            return "Gross: " + Gross.ToString() + ", Net: " + Net.ToString() + ", ExpectedValidationResult: " + ExpectedValidationResult.ToString();

        }

    }

    public static void Main()

    {

        List<Value> values = new List<Value>() {

            new Value(0, 0, true),

            new Value(null, 0, true),

            new Value(0, null, true),

            new Value(null, null, true),

            new Value(-1, 1, false),

            new Value(1, -1, false),

            new Value(10, 5, true),

            new Value(-10, -5, true),

            new Value(-5, -10, false),

            new Value(5, 10, false)

        };

        foreach (var val in values)

        {

            bool result = ValidateGrossAndNet(val.Gross, val.Net);

            Console.WriteLine("Test Passed: " + (result == val.ExpectedValidationResult).ToString() + "; " + val.ToString());

        }

    }

    public static bool ValidateGrossAndNet(decimal? gross, decimal? net)

    {

        if (!gross.HasValue || !net.HasValue)

        {

            return true;

        }

        if (gross == net)

        {

            return true;    

        }

        if (gross < 0 && net > 0 || gross > 0 && net < 0)

        {

            return false;   

        }

        if (gross < 0 && net < gross)

        {

            return false;   

        }

        if (gross > 0 && net > gross)

        {

            return false;   

        }

        return true;

    }

}