Writing%20Windows%20applications%20with%20Visual%20Basic

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Introduction to Visual Basic
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.)


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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 .
Property Example 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
window Click on Floppy A Open the folder Open
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 ltyour namegt 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 button 6. Lock the controls 7. 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 PrintForm 9. Save and run the
project 10. 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
(0s and 1s) 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) Read Summary, Key terms, Review questions