C# Value and Reference Types

In c#, we have two ways to allocate the space in memory, i.e., either on stack or heap memory based on the Value Type or Reference Type parameters.

This seems to be a basic but very important part of C# programming.

1 - C# Value type

Value types are generally (not always) stored on the stack and are passed by copying.

The way in which a variable assignment works differs between reference and value types.

For example, if we define and assign a value to the variable like int x = 12; then the system will use the same memory space of variable ‘x’ to store the value ‘12’.

The following data types are all of value type:

If we have something like:

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

namespace HelloWorld
{
    class Program
    {   
        static void Main(string[] args)
        {
            int v1 = 12;
            int v2 = 22;
            v2 = v1;
            Console.WriteLine(v2);
            Console.ReadLine();
        }
    }
}

Output:

Implementation:

Here, both v1 and v2 will be on the stack and are different entities.

2 - C# Reference Type

A value type is basically stored on the heap and passed by creating a reference.

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

namespace HelloWorld
{
    class A
    {
        public int value
        {
            get;
            set;
        }
        public A(int passbyref)
        {
            this.value = passbyref;
        }
    }
    class Program
    {   
        static void Main(string[] args)
        {
            A v1 = new A(12);
            A v2 = new A(22); //Breakpoint
            v2 = v1;
            Console.WriteLine(v1.value);
            Console.WriteLine(v2.value);
            Console.ReadLine();
        }
    }
}

Output:

Implementation:

v1 and v2 will be on the heap as two entities until a breakpoint.

And after the breakpoint, they both point to one entity.

So, a change in one will affect the other.

The following are the different data types that will fall under Reference Type in c# programming language.

• String
• Class
• Delegates
• All Arrays, Even if their elements are value types

3 - C# Passing Arguments

We have the following four possibilities:

• Pass value type by value.
• pass value type by reference
• pass reference type by value.
• pass reference type by reference.

3. 01 - C# Pass value type by value

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

namespace HelloWorld
{
    struct A
    {
        public int val
        {
            get;
            set;
        }
    }
    class Program
    {
        public static void methodtoshowref(A obj)
        {
            obj = new A();
        }
        static void Main(string[] args)
        {
            A v1 = new A();
            v1.val = 10;
            methodtoshowref(v1);
            Console.WriteLine(v1.val);
            Console.ReadLine();
        }       
    }
}

Output:

10 : because one more copy is created and thus the original is not affected.

3. 02 - C# Pass value type by reference

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

namespace HelloWorld
{
    struct A
    {
        public int val
        {
            get;
            set;
        }
    }
    class Program
    {
        public static void methodtoshowref(ref A obj)
        {
            obj = new A();
        }
        static void Main(string[] args)
        {
            A v1 = new A();
            v1.val = 10;
            methodtoshowref(ref v1);
            Console.WriteLine(v1.val);
            Console.ReadLine();
        }       
    }
}

Output:

0 : since now one copy is shared by both methods.

3. 03 - C# Pass reference type by value (by default)

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

namespace HelloWorld
{
    class A
    {
        public int val
        {
            get;
            set;
        }
    }
    class Program
    {
        public static void methodtoshowref(A obj)
        {
            obj = null;
        }
        static void Main(string[] args)
        {
            A v1 = new A();
            v1.val = 10;
            methodtoshowref(v1);
            Console.WriteLine(v1.val);
            Console.ReadLine();
        }       
    }
}

Output:

10 : this happens because we are passing it by value.

*** Now here if we do, obj.val=1000 then it will print 1000 (this is because passing a variable to a function by value is equivalent to instantiating a new variable and assigning it to the first).

3. 04 - C# Pass reference type by reference

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

namespace HelloWorld
{
    class A
    {
        public int val
        {
            get;
            set;
        }
    }
    class Program
    {
        public static void methodtoshowref(ref A obj)
        {
            obj = null;
        }
        static void Main(string[] args)
        {
            A v1 = new A();
            v1.val = 10;
            methodtoshowref(ref v1);
            Console.WriteLine(v1.val);
            Console.ReadLine();
        }       
    }
}

Output:

An unhandled exception of type 'System.NullReferenceException' occurred in HelloWorld.exe

The error we have now is obj=null so it will give a nullobject error.