ClassVsStructDemo.cs

using System;

namespace ClassVsStructDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            DemoStruct struct1 = new DemoStruct();
            struct1.x = 4;

            DemoStruct struct2 = struct1;
            ref DemoStruct struct3 = ref struct2; //struct2 and struct3 point to the same memory
            IInterfaceDemo struct4 = new DemoStruct(1, 5); //this struct is treated as a reference type

            DemoStruct struct5; //This struct is initialized by hand without using "new"
            struct5.x = 1;
            struct5.y = 2;
            struct5.structArray = null;
            struct5.childObject = null;

            struct5 = GetModifiedStruct(struct5);

            DemoStruct? struct6 = null; // '?' means nullable version of this struct
            if(struct6 != null) { /*This will not run */ } 

            struct6 = new DemoStruct();
            if (struct6.HasValue) //struct6 != null and struct6.HasValue are functionally equivalent
            {
                DemoStruct struct7 = struct6.Value; // .Value throws an exception if .HasValue is false
                struct7.x = 1; //struct7 is a regular non-nullable struct
            }

            DemoClass object1;
            DemoClass object2;

            object1 = new DemoClass(0);
            object2 = object1;

            ModifyObject(object2);
        }

        private static void ModifyObject(DemoClass objectToModify)
        {
            objectToModify.x += 5;
        }

        private static DemoStruct GetModifiedStruct(DemoStruct structToModify)
        {
            structToModify.x += 5;
            return structToModify;
        }
    }

    public struct DemoStruct : IInterfaceDemo
    {
        //public DemoStruct() //Doesn't compile
        //{
        //    x = 5;
        //    y = 5;
        //    structArray = new DemoStruct[999];
        //    childObject = new DemoClass(2);
        //}

        //public DemoStruct(float _x) //Doesn't compile
        //{
        //    x = _x;
        //}

        public DemoStruct(float _x, float _y)
        {
            x = _x;
            y = _y;
            structArray = null;
            childObject = null;
        }

        public float x;
        public float y;
        public DemoStruct[] structArray;
        //public DemoStruct childStruct; //Doesn't compile
        public DemoClass childObject;
        public void InterfaceMethod() { /* DoStuff */ }
    }

    public class DemoClass : IInterfaceDemo
    {
        public DemoClass(float _x)
        {
            x = _x; //Doesn't assign all the member variables
        }

        public float x;
        public float y;
        public DemoStruct[] structArray;
        public DemoStruct childStruct;
        public DemoClass childObject;
        public void InterfaceMethod() { /* DoStuff */ }
    }

    public interface IInterfaceDemo
    {
        public void InterfaceMethod();
    }
}