program.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Oef3Teldezin
{
    class Program
    {
        static void Main(string[] args)
        {
            Business z1 = new Business();
            Console.WriteLine("Geef een zin");
            Console.ForegroundColor = ConsoleColor.Red;
            Console.WriteLine("Aantal woorden in de gegeven zin: " +z1.Aantalwoorden(Console.ReadLine()));
            Console.ReadLine();
        }
    }
}

Business.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Oef3Teldezin
{
    class Business
    {
        public int Aantalwoorden(string pinvoer)
        {
            int aantal = 1;
            for (int teller = 0; teller < pinvoer.Length; teller++)
            {
                if (pinvoer[teller]==' ')
                {
                    aantal += 1;
                }
            }
            return aantal;

        }
    }
}