Csharp/C Sharp/Language Basics/Ref Out

compare the difference between passing a null reference vs. a reference to a zero length string

<source lang="csharp"> using System; public class Class1 {

   public static void Main(string[] strings) {
       Example exampleObject = new Example();
       Console.WriteLine("Pass a null object:");
       string s = null;
       exampleObject.TestString(s);
       Console.WriteLine();
       Console.WriteLine("Pass an empty string:");
       exampleObject.TestString("");
       Console.WriteLine();
       Console.WriteLine("Pass a real string:");
       exampleObject.TestString("test string");
       Console.WriteLine();
   }

} class Example {

   public void TestString(string sTest) {
       if (sTest == null) {
           Console.WriteLine("sTest is null");
           return;
       }
       if (String.rupare(sTest, "") == 0) {
           Console.WriteLine("sTest references an empty string");
           return;
       }
       Console.WriteLine("sTest refers to: "" + sTest + """);
   }

}

</source>

Reference, output and value parameters.

<source lang="csharp">

using System; class ReferenceAndOutputParameters {

  public void aMethod()
  {
     int y = 5; 
     int z; 
     Console.WriteLine( "Original value of y: {0}", y );
     Console.WriteLine( "Original value of z: uninitialized\n" );
     SquareRef( ref y );  
     SquareOut( out z );  
     Console.WriteLine( "Value of y after SquareRef: {0}", y );
     Console.WriteLine( "Value of z after SquareOut: {0}\n", z );
     Square( y );
     Square( z );
     Console.WriteLine( "Value of y after Square: {0}", y );
     Console.WriteLine( "Value of z after Square: {0}", z );
  } 
  void SquareRef( ref int x )
  {
     x = x * x; 
  } 
  void SquareOut( out int x )
  {
     x = 6; 
     x = x * x; 
  } 
  void Square( int x )
  {
     x = x * x;
  }

} class ReferenceAndOutputParamtersTest {

  static void Main( string[] args )
  {
     ReferenceAndOutputParameters test = new ReferenceAndOutputParameters();
     test.aMethod();
  }

}

       </source>

Testing the effects of passing array references by value and by reference.

<source lang="csharp">

using System; public class ArrayReferenceTest {

  public static void Main( string[] args )
  {
     int[] firstArray = { 1, 2, 3 };
     int[] firstArrayCopy = firstArray;
     for ( int i = 0; i < firstArray.Length; i++ )
        Console.Write( "{0} ", firstArray[ i ] );
     FirstDouble( firstArray );
     for ( int i = 0; i < firstArray.Length; i++ )
        Console.Write( "{0} ", firstArray[ i ] );
     if ( firstArray == firstArrayCopy )
        Console.WriteLine("same" );
     else
        Console.WriteLine("different" );
     int[] secondArray = { 1, 2, 3 };
     int[] secondArrayCopy = secondArray;
     for ( int i = 0; i < secondArray.Length; i++ )
        Console.Write( "{0} ", secondArray[ i ] );
     SecondDouble( ref secondArray );
     for ( int i = 0; i < secondArray.Length; i++ )
        Console.Write( "{0} ", secondArray[ i ] );
     if ( secondArray == secondArrayCopy )
        Console.WriteLine("same" );
     else
        Console.WriteLine("different" );
  } 
  public static void FirstDouble( int[] array )
  {
     for ( int i = 0; i < array.Length; i++ )
        array[ i ] *= 2;
     array = new int[] { 11, 12, 13 };
  } 
  public static void SecondDouble( ref int[] array )
  {
     for ( int i = 0; i < array.Length; i++ )
        array[ i ] *= 2;
     array = new int[] { 11, 12, 13 };
  } 

}

       </source>

the out descriptor allows a function a value in an argument without initializing the argument

<source lang="csharp"> using System; public class Test {

   public static void Main(string[] strings) {
       Student student;
       Example example = new Example();
       example.ReturnStudent(out student);
       Console.WriteLine("Student is " + student.name);
   }

} class Example {

   public void ReturnStudent(out Student student) {
       student = new Student();
       student.name = "Jenny";
   }

} public class Student {

   public string name;

}

</source>