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Writing Windows applications with Visual Basic

Figure 1.1

The first program works as follows: (These operations can be performed in any order).1. Type your name in the top text box.2. Type a message in the lower text box.3. Click on one of the Option buttons under Color.4. Click on one or more of the Check buttons under Style.5. Click on Display

Your name and message will appear in the smaller box next to the image, in the selected color and style.)

Introduction to Visual Basic

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The second program works as follows:1. Click on the arrow in the drop-down menu; select one of the choices which appears.2. Click on one of the flavors in the list box.3. Click on the command button.

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The Windows graphical user interface (GUI)In a Visual Basic program, the programmer creates:

- forms (windows) holding controls (buttons, boxes,etc.) - data is entered- output appears

- procedures (chunks of code) for parts of the form

Example Fig. 1.1 Display has a procedure to display the name and message. Green has a procedure to change the name and message to green.

Programming languages - procedural, object-oriented, and event-driven

Older languages (Pascal, FORTRAN, etc.) are procedural languages. For example, input was entered in a fixed order line by line according to prompts (“Enter name”, “Enter style”, etc.)

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In Visual Basic, the user can enter data in any desired order.

Example Click on the Color or Style buttons at any time.

Visual Basic programs are event-driven; they respond to user actions (events). Some events are internal.

Example Event - the user clicks on a button.

The object model An object consists of - data (which has various properties)

- procedures acting on the data (methods)Example Fig. 1.1 Button Italic has

- property checked (True or False)- a method which italicizes the letters in some box

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Syntax (grammar) for property is name of object . PropertyExample optGreen.checked

Syntax for method is name of object . method Example Printer.Print (sends output to the Printer)

Versions of Visual Basic We use Version 5.00.

Writing Visual Basic projects

The three-step process 1. Define the user interface (create the form; define the objects).2. Set the properties (describe the objects).3. Write the Basic code. PLAN BEFORE CODING !!!!!!!!!!!!!!!!!!!!

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1. Design the user interface.- decide which controls to put on the form- decide what each control does- decide where to put the controls- consult with the user to determine

- correctness and completeness- ease of use

2. Plan the properties for each control.

3. Plan the Basic code.

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The Visual Basic Environment

The Visual Basic window (Fig. 1.2) contains several windows

- form window (center of the screen)- project window (on the right)- properties window (lower right)- toolbox (left) (Fig. 1.3)

Note: the toolbox on your screen may not contain all the icons shown on the text.

- toolbar (top) (Fig. 1.4)

Form location and size information are located at the top right of the Visual Basic window.

Help is on the right of the toolbar.

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Miscellaneous - design time is the time spent writing the program- run time is the time when the program runs- break time is the time when the program stops because

- an error has occurred, or - the user has suspended execution

Writing your first Visual Basic project Create the following form (Fig. 1.5)

Hello World by J. C. Bradley

Hello World

Push Me

Exit

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When you click on “Push Me”, the “Hello World” appears.

Set up your Visual Basic workspace A. Create a folder within which you will save your project. (Refer to the handout.)

Note: You must create this folder before you save your project.

B. Launch Visual Basic (refer to the handout)C. Set up your workspace (refer to the handout)

Design the user interface (Fig. 1.9) A. Design the form in complete detail on paper!B. Set up the form in Visual Basic (set size and position)

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C. Place controls on the form(i) Place the “Hello World” label on the form

- from the toolbox select the label icon (the cursor becomes a cross) (Fig. 1.10)

- click where you want the label (Fig. 1.11)

- drag the cursor to draw a box (Fig. 1.12)

(Note: these operations reserve space for the “Hello World” space. You will put the words “Hello World” on the form later. If you wish, you can resize and move the control.)

(ii) Place the “Push Me” and “Exit” buttons on the form (Fig. 1.13 - 1.16)

- from the toolbox select Command button - draw a command button as you drew a label, or

double-click on the Command button

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Note: double-clicking gives buttons of the same size.

- move command buttons to the desired positions- lock the controls (to keep from moving them)

- click on Format (top of page) - select Lock controls

- to unlock controls, do the same

(iii) Set the name and caption properties for the label (Fig. 1.17 - 1.21)

- click once on the label- click on the title bar of the Properties window- scroll down to the Name property and type the

word lblMessage

The word “lblMessage” now appears at the top of the Properties window.

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- scroll down to the Caption property and delete the word Label1

This deletes the word “Label1” from the form. When the program runs, the message “Hello World” will appear here.

(iv) Set the Name and Caption properties for the first command button (Fig. 1.22)

- click on the Command1 button- change the Name property to cmdPush- change the Caption property to Push Me

(v) Set the Name and Caption properties for the second Command button

- change the Name property to cmdExit- change the Caption property to Exit

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(vi) Set the Caption property for the form to the phrase

Hello World by your name (Fig. 1.23)

Visual Basic code statements Remark statements, comments (MOST IMPORTANT!!!)

- three most important features of a program- correctness- READABILITY!!!!

- for others- FOR YOURSELF!!!

- efficiency (usually not important except for graphics

- comments describe what the code does- general description at the beginning

- purpose of the module (chunk of code)- name of programmer (important for a

team of programmers)

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- date written and/or modified- other statements if necessary to describe how

the code works- comments begin with a single quote- comments can appear on the same line as other statements- Example Book p. 20

Assignment statements- assignments place a value into a variable- general form is object . property = value -Example Book p. 20

- lblMessage.Caption = “Hello”- lblTitle.FontSize = 12

- literals (messages, names, etc) are enclosed in “ “- numbers and True or False are not

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The End statement- this statement stops a program - usually End is placed in the Exit module

Code the event procedures for Hello World A. Code the click event for “Push Me” (Fig. 1.25)

- double-click on the “Push Me” button

You will see a new window with part of the code for the appropriate procedure

- hit the tab key and type ‘Display the Hello World message

- hit the Enter key; the comment turns green- hit the Enter key, hit the Tab key, and type

lblMessage.Caption = “Hello World”- close the code window, if you wish

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B. Code the click event for the “Exit” button (Fig. 1.26)- add the comment ‘Exit the program- skip one line- type End

Run the project (Fig. 1.27, 1.28)A. Open Run and select Start (There are also other ways to run programs.) B. Click on “Push Me”.C. Click on “Exit”.

Save the project (Fig. 1.29) A. Under File select Save. (Fig. 1.30- 1.32)B. Move to the correct folder. C. Type in a file name. D. Hit Enter or click Save.

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Open the project (Note: this screen is different from Fig. 1.32)

We assume that Visual Basic is not open.

Under File choose Open Select the tab that says Existing Click on the arrow next to the folder name near the top of the windowClick on Floppy A Open the folderOpen the project

If the form does not show up on the screen- in the Properties window open the Form folder- click on the name of the form

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Modify the project 1. Change the size and alignment of the message

- make sure the controls are not locked- enlarge the label

- click on the label- widen the label on both ends

- change the font- select Font property in the Properties box (Fig. 1.33)- click on the dialogue box- select 12 point or larger

-select Alignment and select 2-Center 2. Add a new label for your name

- create a new label on the form- change the Caption to read “by <your name>“

3. Change the Push Me button- select Push Me - change the Caption to English

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4. Add a Spanish button - create a new command button- change the Name to cmdSpanish-change the Caption to Spanish

5. Add a Print button6. Lock the controls7. Add code for the Spanish button

- double-click on the Spanish button- type in ‘ Display the Hola Mundo Message

lblMessage.Caption = “Hola Mundo”8. Add code for the Print button

- double-click on the Print button- type in ‘Print the form

PrintForm9. Save and run the project10. Add general remarks in the general declarations section

name of project, name of programmer, date, purpose

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Explore the code window (Fig. 1.37, 1.38)- go to the general section- go to the cmdSpanish section, etc.

Print the project - under File select Print - click the appropriate boxes (Fig, 1.39)

- form image prints a picture of the form (Fig 1.40)- form as text prints a verbal description of the form- code prints the code

Sample printout P. 32-35

Finding and fixing errors Compile errors Before a program runs, it must be translated into machine code (0’s and 1’s) which is all the machine can directly handle.

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Definition A compiler is a program that translates your program into machine language. The process of translating a program into machine language is called compiling.Errors that prevent the program from compiling are called compile errors, or compile-time errors.

Example If you run the program and get a message such as “Method not available”, then this is a compile-time error.

Run-time errors Definition If the program runs and then stops unexpectedly, then the error which causes it to stop is called a run-time error.

Example At some point, you compute the value A/B, and you set B = 0.

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Logic errors Definition A logic error is an error which does not prevent the program from running but which causes an incorrect value to be returned.

Example You compute weekly wage as wage * 400 instead of wage * 40.

Visual Basic highlights compile-time and run-time errors as the program is running. You can fix them and continue running the program by selecting Restart (under Run).

Project debugging (error correcting)Definition Testing a program is finding errors.

NOTE: If you run a program and find no errors, then your test is UNSUCCESSFUL!!!

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Naming conventions - names for controls

- Names for labels begin with lbl- Names for command buttons begin with cmd- Names for forms begin with frm

- names must not be Command1, Label1, etc. - names must not be numbers

Visual Basic files When you save your project, you get

- a project file (name . VBP)- a code file (name . BAS)- a form file (name . FRM)- a custom control file (name . VBX)

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