PrePost Operators

Such short-circuit evaluations save processing cycles and improve code performance by eliminating unnecessary code execution. The code in Listing 3.3 shows various short circuit evaluations in action.

Listing 3.3. Understanding How Short Circuit Evaluations Work

using System;

   namespace ShortCircuitEvaluation



{


/// <summary>
       /// Summary description for Class1.
       /// </summary>
       class Class1     {

           static bool ReturnsTrue( ) {
               Console.WriteLine( "*********[ EXECUTING ReturnsTrue ]***********" );
               return true;
           }

           static bool ReturnsFalse( ) {
               Console.WriteLine( "*********[ EXECUTING ReturnsFalse ]***********" );
               return false;
           }
           /// <summary>
           /// C# short Circuit evaluation example
           /// </summary>
           [STAThread]
           static void Main(string[] args)    {


               Console.WriteLine( "true AND ReturnsTrue( )" );
               if( true && ReturnsTrue( ) ) {
                   Console.WriteLine( "Evaluated trueExpression " +
                      "and executed ReturnsTrue( )" );
               }

               Console.WriteLine( System.Environment.NewLine );

               Console.WriteLine( "true AND ReturnsFalse( )" );
               if( true && ReturnsFalse( ) ) {
                   Console.WriteLine( "This won't execute" );
               } else {
                   Console.WriteLine( "Evaluated trueExpression " +
                      "and executed ReturnsFalse( )" );
               }

               Console.WriteLine( System.Environment.NewLine );

               Console.WriteLine( "true OR True evaluation" );
               if( true  ReturnsTrue( ) ) {
                   Console.WriteLine( "Evaluated only trueExpression " +
                      "then short circuit. ReturnsTrue( ) was not executed" );
               }

               Console.WriteLine( System.Environment.NewLine );

               Console.WriteLine( "true OR ReturnsFalse( )" );
               if( true  ReturnsFalse( ) ) {
                   Console.WriteLine( "Evaluated only trueExpression "+
                      "then short circuit. ReturnsFalse( ) was not executed" );
               }

               Console.WriteLine( System.Environment.NewLine );

               Console.WriteLine( "false AND ReturnsTrue( )" );
               if( false && ReturnsTrue( ) ) {
                   Console.WriteLine( "This won't execute" );
               } else {
                   Console.WriteLine( "Evaluated only falseExpression. "+
                      "ReturnsTrue( ) was not executed" );
               }

               Console.WriteLine( System.Environment.NewLine );

               Console.WriteLine( "false OR ReturnsTrue( )" );
               if( false  ReturnsTrue( ) ) {
                   Console.WriteLine( "Evaluated both false and ReturnsTrue()" );
               }
           }
       }
   }

The code in Listing 3.3 exercises the short-circuit evaluation feature of C#. The best way to understand what is happening in the code is to set a breakpoint on line 27 and begin stepping through the code. Remember, to set a breakpoint, place the cursor on the source line and press F9 or left-click in the channel for the line. To single step the execution, press F11, which allows for stepping into method calls.

Using the Ternary Operator

The ternary operator is a very compact version of an if / else statement. Although a handy shortcut, overuse of the ternary operator can lead to very terse code and should be used only when really needed for very simple expressions. The syntax for the ternary operator is as follows:

result = <expression> ? <statement 1> : <statement 2>;

When the expression is true, statement 1 is executed; otherwise, statement 2 is executed. Notice that the ternary operator expects to return a result. So, for implementing "if order total > 1000, apply 10% discount; else 5% discount" would be implemented as follows:

double discount = orderTotal > 1000 ? .10 : .5;

I suggest that using the ternary operator should not create expressions any more complex than the previous example. After all, the statements being executed can in fact be as complex as another nested ternary operator. For instance, consider the following:

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double discount = preferredCustomer ? orderTotal > 1000 ? .10 : .05 : orderTotal > 2000

"+" ? .1 : .025;

Any idea what that snippet of code does? Create a small project and type in the code to see what it does. Again, the key point is to develop readable code, not cryptic code.

The switch Statement

The idea of the switch statement is to alleviate excessive if statements and to offer a clean approach to handling multiple conditions for a given expression. The switch statement can be thought of as a multiple-choice-style statement. The syntax for the switch statement is as follows:

switch(

expression

) {
  case

const-expression-1

:

one or more statements

;
        break;
  case

const-expression-2

:

one or more statements

;
         break;
  case

const-expression-3

:

one or more statements

;
        break;
  .
  .
  .
  default:

one or more statements

;
     break;
}

The expression to be evaluated can be an integer, character, string, or enum. Each case statement expression must be a const value, meaning that it is defined at compile time and not runtime. For instance, the case expression cannot be the result of a method call or a variable that can change its value.

The switch statement evaluates each case statement until a match is found. If no match is found, the default case is used. The default case is not required, but allows for a catch-all case for evaluation. There are a few things about the switch statement to keep in mind:

• Each case statement that contains statements must have a break statement. This includes the default case.

• Cases can fall through only if the case is empty, meaning that it does not have statements within its body.

• To jump from one case statement to another, the dreaded goto statement is used.

NOTE

The statements within each case block can be any valid C# statement, including method calls and return statements. However, it is best to keep the code within each case short and simple by keeping the number of statements to a minimum.

Again, the main purpose of the switch statement is to provide a cleaner mechanism than using multiple if - else - if combinations. Consider the following two listings. Listing 3.4 uses multiple if - else - if statements for evaluation, whereas Listing 3.5 uses the switch statement to accomplish the same task.

Listing 3.4. Unnecessary Clutter with if-else-if Statement

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using System;

namespace ifelseif {
    /// <summary>
    /// Cluttered ifelseif sample
    /// </summary>
    class Class1 {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main(string[] args) {
            Console.Write( "Enter the type of pet " +" you own: (example dog, cat, fish,

bird)" );
            string animal = Console.ReadLine( );

            if( animal.ToLower( ).Equals( "dog" ) ) {
                Console.WriteLine( "Bark Bark" );
            } else if( animal.ToLower( ).Equals( "cat" ) ) {
                Console.WriteLine( "Meow" );
            } else if( animal.ToLower( ).Equals( "fish" ) ) {
                Console.WriteLine( "swim" );
            } else if( animal.ToLower( ).Equals( "bird" ) ) {
                Console.WriteLine( "Poly want a cracker" );
            } else {
                    Console.WriteLine( "Nice pet" );
                }
        }
    }
}

Listing 3.5. Using the switch Statement to Improve Readability

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using System;
namespace SwitchStatement {

    class Class1 {

        /// <summary>
        ///Demonstrates the usage of the switch statement
        /// </summary>
        [STAThread]
        static void Main(string[] args) {
            Console.Write( "Enter the type of pet" +" you own: (example dog, cat, fish,

bird)" );
            string animal = Console.ReadLine( );

            switch( animal.ToLower( ) ) {
                case "dog":
                    Console.WriteLine( "Bark Bark" );
                    break;
                case "cat":
                    Console.WriteLine( "Meow" );
                    break;
                case "fish":
                    Console.WriteLine( "swim" );
                    break;
                case "bird":
                    Console.WriteLine( "Poly want a cracker" );
                    break;
                default:
                    Console.WriteLine( "Nice pet" );
                    break;
             }
         }
     }
 }