C# Online Compiler | .NET Fiddle

using System;
					
public class Program
{
	public static void Main()
	{
		A a = new A();
		Console.WriteLine(a.value);
		
		setValue(a,1);
		Console.WriteLine(a.value);
		
		newSetValue(a,2);
		Console.WriteLine(a.value);
		
		newRefSetValue(ref a,3);
		Console.WriteLine(a.value);
	}
	
	public static void setValue(A a,int value)
	{
		a.value = value;
	}
	
	public static void newSetValue(A a, int value)
	{
		a = new A();
		a.value = value;
	}
	
	public static void newRefSetValue(ref A a, int value)
	{
		a = new A();
		a.value = value;
	}
}

public class A
{ 
	public A()
	{
		value = 0;
	}
	public int value { get; set; }
}