1. T U T O R I A L  2009 Pearson Education, Inc. All rights reserved. 1 13 Enhancing the Wage Calculator Application Introducing Function Procedures and Sub Procedures

2.  2009 Pearson Education, Inc. All rights reserved. 2 Outline 13.1 Test-Driving the Enhanced Wage Calculator Application 13.2 Classes and Procedures 13.3 Function Procedures 13.4 Using Sub Procedures in the Wage Calculator Application 13.5 Using the Debugger: Debugging Controls 13.6 Optional Parameters

3.  2009 Pearson Education, Inc. All rights reserved. 3 In this tutorial you will learn: ■Construct applications modularly from pieces called procedures. ■Work with “ built-in ” procedures. ■Distinguish between Function procedures and Sub procedures, and determine when each should be used. ■Create your own Function procedures and Sub procedures. ■Use the Debugging controls on the Standard Toolbar. Objectives

4.  2009 Pearson Education, Inc. All rights reserved. 4 ■The best way to develop and maintain a large application is to construct it from smaller, more manageable pieces. – This technique is known as divide and conquer (also called componentization). ■Manageable pieces include program components—known as procedures. Introduction

5. Application Requirements  2009 Pearson Education, Inc. All rights reserved. 5 13.1 Test-Driving the Enhanced Wage Calculator Application A payroll company calculates the gross earnings per week of employees. Employees’ weekly salaries are based on the number of hours they worked and their hourly wages. Create an application that accepts this information and calculates each employee’s total earnings. The application assumes a standard work week of 40 hours. The wages for 40 or fewer hours are calculated by multiplying the employee’s hourly wage by the number of hours worked. Any time worked over 40 hours in a week is considered “overtime” and earns time and a half. Salary for time and a half is calculated by multiplying the employee’s hourly wage by 1.5 and multiplying the result of that calculation by the number of overtime hours worked. The total overtime earned is added to the user’s gross earnings for the regular 40 hours of work to calculate the total earnings for that week.

6.  2009 Pearson Education, Inc. All rights reserved. 6 Test-Driving the Enhanced Wage Calculator Application ■Run the completed application (Fig. 13.1). Figure 13.1 | Wage Calculator running. ■Click the Calculate Button. The result ( $475.00 ) is displayed in the Gross earnings: Label.

7.  2009 Pearson Education, Inc. All rights reserved. 7 ■The key to creating large applications is to break them into smaller pieces. ■In object-oriented programming, these pieces consist primarily of classes, which can be further broken down into methods. ■Programmers combine programmer-defined classes and methods with preexisting code in the.NET Framework Class Library. –Using preexisting code saves time, effort and money. –The concept of reusing code increases efficiency for application developers. 13.2 Classes and Procedures

8.  2009 Pearson Education, Inc. All rights reserved. 8 13.2 Classes and Procedures (Cont.) ■Figure 13.2 explains several pre-existing Visual Basic methods. Figure 13.2 | Some predefined Visual Basic methods. (Part 1 of 2.)

9.  2009 Pearson Education, Inc. All rights reserved. 9 13.2 Classes and Procedures (Cont.) Figure 13.2 | Some predefined Visual Basic methods. (Part 2 of 2.)

10.  2009 Pearson Education, Inc. All rights reserved. 10 Creating the Hypotenuse Calculator Application ■Open HypotenuseCalculator.sln in the HypotenuseCalculator directory (Fig. 13.3). Figure 13.3 | Hypotenuse Calculator GUI.

11.  2009 Pearson Education, Inc. All rights reserved. 11 Creating the Hypotenuse Calculator Application (Cont.) ■The event handler for the Calculate Hypotenuse Button is incomplete (Fig. 13.4). Figure 13.4 | Hypotenuse Calculator template code. Lengths for sides A, B and hypotenuse Square of lengths for sides A, B and hypotenuse Message dialog displays if negative values (or non- numeric values) are entered

12.  2009 Pearson Education, Inc. All rights reserved. 12 Creating the Hypotenuse Calculator Application (Cont.) ■The procedure begins in line 28 (Fig. 13.5) with keyword Function, followed by a procedure name Figure 13.5 | Hypotenuse Calculator GUI. Function procedure header End Function keywords mark the end of a Function procedure

13.  2009 Pearson Education, Inc. All rights reserved. 13 Software Design Tip To promote reusability, each procedure should perform a single well-defined task, and the procedure name should express that task effectively and concisely.

14.  2009 Pearson Education, Inc. All rights reserved. 14 Good Programming Practice Choosing meaningful procedure names and parameter names makes applications more readable and reduces the need for excessive comments.

15.  2009 Pearson Education, Inc. All rights reserved. 15 ■The procedure name is followed by a set of parentheses containing a parameter declaration. –The declaration in the parentheses is known as the parameter list, –Variables (called parameters) are declared, enabling a procedure to receive data that helps the procedure perform its task. –The parameter list can contain zero or more declarations separated by commas. Creating the Hypotenuse Calculator Application (Cont.)

16.  2009 Pearson Education, Inc. All rights reserved. 16 ■A Function procedure returns one value after it performs its task. ■To specify the return type, the parameter list is followed by the keyword As, which is in turn followed by a data type. ■The Function procedure ends with the keywords End Function. Creating the Hypotenuse Calculator Application (Cont.)

17.  2009 Pearson Education, Inc. All rights reserved. 17 Good Programming Practice Procedure names should be verbs and should begin with an uppercase first letter. Each subsequent word in the name should begin with an uppercase first letter. This naming convention is known as Pascal case.

18.  2009 Pearson Education, Inc. All rights reserved. 18 Creating the Hypotenuse Calculator Application (Cont.) ■The ^ operator (Fig. 13.6) is used to calculate the square of input. ■A Return statement is used to return this value. Figure 13.6 | Square procedure definition. Calculate the square using the ^ operator

19.  2009 Pearson Education, Inc. All rights reserved. 19 Good Programming Practice Placing a blank line between procedure definitions enhances application readability.

20.  2009 Pearson Education, Inc. All rights reserved. 20 Creating the Hypotenuse Calculator Application (Cont.) ■These lines call Square by using the procedure name followed by a set of parentheses that contain the procedure’s argument (Fig. 13.7). Figure 13.7 | Invoking procedure Square. Calling procedure Square

21.  2009 Pearson Education, Inc. All rights reserved. 21 Creating the Hypotenuse Calculator Application (Cont.) ■Note that typing the opening parenthesis causes the Visual Basic IDE to display a window containing the procedure’s argument names and types (Fig. 13.8). ■This is the Parameter Info feature of the IDE. Figure 13.8 | Parameter Info window. Parameter Info window

22.  2009 Pearson Education, Inc. All rights reserved. 22 Good Programming Practice Selecting descriptive parameter names makes the information provided by the Parameter Info feature more meaningful.

23.  2009 Pearson Education, Inc. All rights reserved. 23 ■A procedure is invoked by a procedure call. –The procedure call specifies the procedure name and provides arguments that the called procedure requires to do its job. –Each argument is assigned to one of the procedure’s parameters when the procedure is called. –The number of arguments in the call must match the number of parameters in the definition. –After completing its task, the called procedure returns control to the caller. Creating the Hypotenuse Calculator Application (Cont.)

24.  2009 Pearson Education, Inc. All rights reserved. 24 ■Keyword ByVal indicates that a copy of the argument’s value should be passed to Square. – Square receives the copy of the value input by the user and stores it in the parameter input. –When the Return statement in Square is reached, the value to the right of keyword Return is returned to the point in line 23 where Square was called. –The procedure ’ s execution completes, and the parameter that was holding the copy of the value is discarded. –Program control also transfers to this point, and the application continues. Creating the Hypotenuse Calculator Application (Cont.)

25.  2009 Pearson Education, Inc. All rights reserved. 25 Creating the Hypotenuse Calculator Application (Cont.) ■Line 32 (Fig. 13.9) calls the.NET Framework Class Library method Sqrt of class Math. Figure 13.9 | Completing the calculateButton_Click event handler.

26.  2009 Pearson Education, Inc. All rights reserved. 26 Error-Prevention Tip Small procedures are easier to test, debug and understand than large ones.

27.  2009 Pearson Education, Inc. All rights reserved. 27 Creating the Hypotenuse Calculator Application (Cont.) ■Run and test the application (Fig. 13.10). Figure 13.10 | Hypotenuse Calculator application running.

28.  2009 Pearson Education, Inc. All rights reserved. 28 Creating a Function Procedure That Returns the Largest of Three Numbers ■Open Maximum.sln in the Maximum directory (Fig. 13.11). Figure 13.11 | Maximum application in Design view. TextBoxes used to input three values

29.  2009 Pearson Education, Inc. All rights reserved. 29 Creating a Function Procedure That Returns the Largest of Three Numbers (Cont.) ■Double click the Maximum Button to create an event handler. ■Note that Maximum has been underlined in blue, because Function procedure Maximum has not yet been defined (Fig. 13.12). Figure 13.12 | Invoking Function procedure Maximum. Calling a procedure that has not yet been defined is an error

30.  2009 Pearson Education, Inc. All rights reserved. 30 Common Programming Error Calling a procedure that does not yet exist or misspelling the procedure name in a procedure call results in a compilation error.

31.  2009 Pearson Education, Inc. All rights reserved. 31 Creating a Function Procedure That Returns the Largest of Three Numbers (Cont.) ■Create the Function procedure Maximum (Fig. 13.13). Figure 13.13 | Maximum Function procedure. Empty Function procedure Maximum

32.  2009 Pearson Education, Inc. All rights reserved. 32 ■The maximum is determined by using the Max method of.NET Framework Class Library class Math (Fig. 13.14). ■The Return statement terminates execution of the procedure and returns the result of finalMaximum. Creating a Function Procedure That Returns the Largest of Three Numbers (Cont.) Figure 13.14 | Math.Max returns the larger of its two arguments. Calling Math.Max to determine the maximum of two values

33.  2009 Pearson Education, Inc. All rights reserved. 33 Creating a Function Procedure That Returns the Largest of Three Numbers (Cont.) ■Run and test the application (Fig. 13.15). Figure 13.15 | Maximum application running.

34.  2009 Pearson Education, Inc. All rights reserved. 34 Creating a Sub Procedure within the Wage Calculator Application ■Open WageCalculator2.sln in the WageCalculator2 directory. ■Double click the Calculate Button to generate an event handler (Fig. 13.16). Figure 13.16 | calculateButton_Click calls DisplayPay. Call to DisplayPay

35.  2009 Pearson Education, Inc. All rights reserved. 35 ■Add Sub procedure DisplayPay to your application (lines 18–39 of Fig. 13.17). ■There is no return type, because Sub procedures do not return values. ■When control reaches the End Sub statement, control returns to the calling procedure. Creating a Sub Procedure within the Wage Calculator Application (Cont.)

36.  2009 Pearson Education, Inc. All rights reserved. 36 Creating a Sub Procedure within the Wage Calculator Application (Cont.) Figure 13.17 | Sub procedure DisplayPay definition. DisplayPay calculates and displays the user’s gross earnings

37.  2009 Pearson Education, Inc. All rights reserved. 37 Creating a Function Procedure within the Wage Calculator Application ■Note that the return type of the procedure is Boolean (Fig. 13.18)—the value returned by the procedure must be a Boolean. Figure 13.18 | Function procedure CheckOverTime definition. CheckOvertime determines if the user has worked overtime

38.  2009 Pearson Education, Inc. All rights reserved. 38 Common Programming Error Failure to return a value from a Function procedure causes the procedure to return the default value for the return-type ( 0 for numeric types, False for Booleans, Nothing for so-called reference types), often resulting in logic errors.

39.  2009 Pearson Education, Inc. All rights reserved. 39 Creating a Function Procedure within the Wage Calculator Application (Cont.) ■In Sub procedure DisplayPay, replace the statement on line 26 (Fig. 13.19). Figure 13.19 | DisplayPay calls Function procedure CheckOvertime. Call to procedure CheckOvertime

40.  2009 Pearson Education, Inc. All rights reserved. 40 ■Figure 13.20 presents the source code of the application. Outline (1 of 3 ) Call to Sub procedure that calculates and displays wages

41.  2009 Pearson Education, Inc. All rights reserved. 41 Outline (2 of 3 ) Call to Function procedure that determines if user has worked overtime Sub procedure header specifies parameter names and types

42.  2009 Pearson Education, Inc. All rights reserved. 42 Outline (3 of 3 ) End Sub keywords indicate the end of Sub procedure definition Function procedure header specifies parameter names and types as well as a return type End Function keywords indicate the end of Function procedure definition

43.  2009 Pearson Education, Inc. All rights reserved. 43 13.5 Using the Debugger: Debugging Controls ■These ToolStripButton s (Fig. 13.21) provide convenient access to commands in the Debug menu. Figure 13.21 | Debugging controls on the Standard toolbar. Start DebuggingStep IntoStep Out Pause execution Stop Debugging Step Over

44.  2009 Pearson Education, Inc. All rights reserved. 44 Using the Debugger: Debugging Controls ■In the Wage Calculator application, set a breakpoint in line 15 (Fig. 13.22). ■Select Debug > Start Debugging. Enter the value 7.50 in the Hourly wage: TextBox, and enter 35 in the Weekly hours: TextBox. Click the Calculate Button Figure 13.22 | Setting a breakpoint. Breakpoint set at a line containing a procedure call

45.  2009 Pearson Education, Inc. All rights reserved. 45 ■The Step Into ToolStripButton ( ) executes the next statement in the application (Fig. 13.23). –If the next statement to execute is a procedure call, control is transferred to the called procedure. –The Step Into ToolStripButton allows you to enter a procedure and confirm its execution. Figure 13.23 | Statement calls procedure DisplayPay. Next statement to execute is a procedure call Using the Debugger: Debugging Controls (Cont.)

46.  2009 Pearson Education, Inc. All rights reserved. 46 ■Click the Step Into ToolStripButton to enter procedure DisplayPay (Fig. 13.24). Figure 13.24 | Using the Standard toolbar’s Step Into ToolStripButton. Control transfers to the procedure definition Using the Debugger: Debugging Controls (Cont.)

47.  2009 Pearson Education, Inc. All rights reserved. 47 ■Click the Step Over ToolStripButton ( ) to execute the current statement without stepping into it (Fig. 13.25). Figure 13.25 | Using the Standard toolbar’s Step Over ToolStripButton. Procedure CheckOverTime executes without stepping into it when you click the Step Over ToolStripButton Using the Debugger: Debugging Controls (Cont.)

48.  2009 Pearson Education, Inc. All rights reserved. 48 ■Click the Step Over ToolStripButton again. – Step Over behaves like the Step Into when the next statement to execute does not contain a procedure call. –If the next statement to execute contains a procedure call, the called procedure executes in its entirety, and the yellow arrow advances to the next executable line (Fig. 13.26). Figure 13.26 | Using the Standard toolbar’s Step Over ToolStripButton again. Using the Debugger: Debugging Controls (Cont.)

49.  2009 Pearson Education, Inc. All rights reserved. 49 ■Set a breakpoint at the end of procedure DisplayPay in line 39 (Fig. 13.27). Figure 13.27 | Using the Standard toolbar’s Continue ToolStripButton. Using the Debugger: Debugging Controls (Cont.)

50.  2009 Pearson Education, Inc. All rights reserved. 50 ■Clicking the Continue ToolStripButton ( ) executes any statements between the next executable statement and the next breakpoint or the end of the current event handler. ■Click the Stop Debugging ToolStripButton ( ). Using the Debugger: Debugging Controls (Cont.)

51.  2009 Pearson Education, Inc. All rights reserved. 51 ■When a procedure is invoked repeatedly with the same argument value, you can specify that such a parameter is an Optional parameter. ■When the argument for an Optional parameter is omitted, the compiler rewrites the procedure call, inserting the default value. ■There are three rules for using Optional parameters: –Each Optional parameter must have a default value. –The default value must be a constant expression. –All parameters after an Optional parameter must also be Optional parameters. 13.6 Optional Parameters

52.  2009 Pearson Education, Inc. All rights reserved. 52 ■Consider the Function BoxVolume : Function BoxVolume( Optional ByVal length As Integer = 1, _ Optional ByVal width As Integer = 1, _ Optional ByVal height As Integer = 1 ) As Integer Return length * width * height End Function ' BoxVolume ■Each parameter has a default value specified with an = and a literal value ( 1 ). 13.6 Optional Parameters (Cont.)

53.  2009 Pearson Education, Inc. All rights reserved. 53 ■You can now invoke Function BoxVolume several different ways: BoxVolume() ' returns 1; default values used for length, width, height BoxVolume(10) ' returns 10; default values used for width, height BoxVolume(10, 20) ' returns 200; default value used for height BoxVolume(10, 20, 30) ' returns 6000; no default values used BoxVolume(, 20, 30) ' returns 600; default value used for length BoxVolume(10,, 30) ' returns 300; default value used for width ■Comma placeholders are used when an omitted argument is not the last argument in the call. 13.6 Optional Parameters (Cont.)