Work with "out" and "ref" keywords in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace simplevalue
{
    class Progra
 {
      static void Addvalue(int val)
        {
             val++
        }
      static void Main(string[] args)
       {
            int value = 10;
            Addvalue(value);
            Console.WriteLine(value);
            Console.Read();
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace outexample
{
    class Program
    {
        static void value(out int val)
        {
           val = 20;
        }
    static void Main(string[] args)
        {
            int value;
            value(out value);
            Console.WriteLine(value);    
           Console.Read();
        }
    }
}

"ref" keyword

The ref keyword on a method parameter causes a method to refer to the same variable that was ed as an input parameter for the same method. If you do any changes to the variable, they will be reflected in the variable.

The ref keyword is similer to out keyword but ref requires that the variable be initialized before being ed.

For example

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace outexample
{
    class Program
    {
        static void value(ref int val)
        {
           val = 20;
        }
    static void Main(string[] args)
        {
            int value;
            value(ref value);
            Console.WriteLine(value);    
           Console.Read();
        }
    }
}

when we build this code it will fire an error "use of unassigned local variable 'value' " the resion is behind that the ref requires that the variable be initialized before being ed.

To run above program properly just initialized the value (variable).

For example

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace outexample
{
    class Program
    {
        static void value(ref int val)
        {
           val = 20;
        }
    static void Main(string[] args)
        {
            int value = 10;
            value(ref value);
            Console.WriteLine(value);    
           Console.Read();
        }
    }
}

Output: 20

Some more useful facts about ref and out keyword

The ref and out keywords are treated differently at run-time, but they are treated the same at compile time. Therefore methods cannot be overloaded if one method takes a ref argument and the other takes an out argument. These two methods, for example, are identical in terms of compilation, so this code will not compile

class Program
{
    // compiler error CS0663: "cannot define overloaded
    // methods that differ only on ref and out"
    public void value(out int i) { }
    public void value(ref int i) { }
}

Overloading can be done, however, if one method takes a ref or out argument and the other uses neither, like this:

class Program
{
    public void value(int i) {  }
    public void value(out int i) {  }
}

Declaring an out method is useful when you want a method to return multiple values. A method that uses an out parameter can still a variables as a return type (see return) but it can also return one or more objects to a calling method as out parameters. This example uses out to return three variables with a single method call. Note that the third argument is assigned to null. This allows methods to return values optionally.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace outexample
    class Program
    {
         static void value(out int i,out string s1,out string s2)
         {
          i=20;
          s1="I've been returned";
          s2=null;
        
         }
       
        static void Main(string[] args)
        {
            int v;
            string str1,str2;
            value(out v,out str1,out str2);
            Console.WriteLine(v +" " + str1 +" "+ str2);
            Console.Read();
        }
    }
}

Output: 20 I've been returned

Properties are not variables and therefore cannot be ed as out parameters.

Final conclusion

The out and the ref parameters are used to return values in the same variables, that you an argument of a method. These both parameters are very useful when your method needs to return more than one values.