C#, I want the main thread output the "num" after all sub-thread end, how to do so? Now I can only get '0'

Question

class Program
    {
        static void AddNumber1(ref int num)
        {
            num++;
        }
        static void AddNumber2(ref int num)
        {
            num++;
        }
        static void Main(string[] args)
        {
            //var mre = new ManualResetEvent(false);
            int num = 0;

            var th1 = new Thread(() =>
            {
                for (int i = 1; i <= 10; i++)
                {
                    AddNumber1(ref num);
                }
            });

            var th2 = new Thread(() =>
            {
                for (int i = 1; i <= 10; i++)
                {
                    AddNumber1(ref num);
                }
            });

            th1.Start();
            th2.Start();

            Console.WriteLine(num);

            Console.Write("Press any key to end :");
            Console.ReadKey(true);
        }

Answer 1

You also could use Tasks instead of Threads like

var th1 = Task.Run(() =>
{
    for (int i = 1; i <= 10; i++)
    {
        AddNumber1(ref num);
    }
});

var th2 = Task.Run(() =>
{
    for (int i = 1; i <= 10; i++)
    {
        AddNumber1(ref num);
    }
});

Task.WaitAll(th1, th2);

Console.WriteLine(num);