Ternary operator in C # and IIf in VB.NET. They are not equal.

A fairly widespread confusion out there is thinking that Visual Basic IIf function corresponds to the ternary operator in C #. Nothing is further from reality, then we will see an example that will show the subtle but important difference between the two ...

The following C # code works perfectly (or almost), in the example we try to assign a nullable date type variable input text using the ternary operator :

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

 namespace ConsoleApplication1
 {
     class Program 
      {
         static void Main (string [] args)
         {
             DateTime?  date = null;
 
             Console. WriteLine ("Put the date (dd / mm / yyyy):");
             string input = Console. ReadLine (); 

             date = (String. IsNullOrEmpty (input)? 
  null: (DateTime?) Convert. ToDateTime (input));

             Console. WriteLine (fecha.ToString ());            
             Console. WriteLine ("Press [S] to repertoire");
             repeat string = Console. ReadLine ();
             if (repeat == "S")
                 Main (args);

         }        
     }
 } 

The program runs without problems (provided you enter an expression valid date!). However, if you do the same with VB.NET, using the IIf function we get an error at runtime:

 Sub Main ()

         Dim time As DateTime?  = Nothing 
          Console. WriteLine ("Put the date (dd / mm / yyyy):")
         Dim input As String = Console. ReadLine

         date = IIf (String. IsNullOrEmpty (input), Nothing, Convert. ToDateTime (input))

         Console. WriteLine (fecha.ToString)
         Console. ReadLine ()
         Console. WriteLine ("Press S for repertoire")
         Dim As String = Console again. ReadLine
         If (repeat = "S") Then 
              Main ()
         End If 
      End Sub 
 

The exception we get is the following:

String Was Not Recognized as a valid DateTime.

The reason is very basic mistake is that the ternary operator is an operator ...!, And IIf function is a function...! Surprise !!!!. That is, while the ternary operator is a symbol that the compiler performs the function invoked at runtime when invoked ... and evaluates all of its parameters, so that conversion to date - Convert.ToDateTime (input) - is performed regardless of the value of the variable (and is empty if it does not contain a valid expression for conversion to date, so that at runtime produces a FormatException.

In short, very careful with using the IIf function ...