Ministry of Higher Education And
Scientific Research
Babylon University
College of Material Engineering
Subject: Programming in Visual Basic
Polymer Engineering Department
2015-2016
Language
Class: Second Year
Lecturer: Hussein Mohammed Salman
Lecture-7: Variables and Constants
Variables are locations in memory used by Visual Basic to hold data and/or information
needed by your application.
Rules used in naming variables:
1. Must begin with letter.
2. Can’t contain an embedded type-declaration character.
3. Must not exceed 255 characters.
4. They can’t be the same as restricted keywords (a restricted keyword is a
word that Visual Basic uses as part of its language. This includes predefined
statements such as “If and Loop”, functions such as “Len and Abs”, and
operators such as “Or and Mod”).
Visual Basic Data Types
Variable Declaration
There are three ways for a variable to be typed (declared):
1. Default
2. Implicit
3. Explicit
1: Default If variables are not implicitly or explicitly typed, they are assigned the
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Ministry of Higher Education And
Scientific Research
Babylon University
College of Material Engineering
Subject: Programming in Visual Basic
Polymer Engineering Department
2015-2016
Language
Class: Second Year
Lecturer: Hussein Mohammed Salman
variant type by default. The variant data type is a special type used by Visual Basic that
can contain numeric, string, or date data.
2:Implicitly To implicitly type a variable, use the corresponding suffix shown above in the
data type table. For example,
TextValue$ = "This is a string" creates a string variable, while
Amount% = 300 creates an integer variable.
3:Explicitly There are many advantages to explicitly typing variables. Primarily, we
insure all computations are properly done, mistyped variable names are easily spotted,
and Visual Basic will take care of insuring consistency in upper and lower case letters
used in variable names. Because of these advantages, and because it is good
programming practice, we will explicitly type all variables.
Static Function total (num)
This makes all the variables in the procedure static regardless of whether they are
declared with Static, Dim, and Private. You can place Static in front of any Sub or
Function Procedure heading, including event procedures and those declared as
Private.
Constants: Constant also store values, but as the name implies, those values
remains constant throughout the execution of an application. Using constants can
make your code more readable by providing meaningful names instead of
numbers. There are a number of built –in constants in Visual Basic. There are two
sources for constants:
 System-defined constants are provided by applications and controls. Visual
Basic constants are listed in the Visual Basic (VB).
 User-defined constants are declared using the Const statement. It is a space in
memory filled with fixed value that will not be changed. For example:
Const X=3.14156
Private Const X=3.14156
Public Const X=3.14156
Constant for procedure
Constant for form and all procedure
Constant for all forms
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Ministry of Higher Education And
Scientific Research
Babylon University
College of Material Engineering
Subject: Programming in Visual Basic
Polymer Engineering Department
2015-2016
Language
Class: Second Year
Lecturer: Hussein Mohammed Salman
Visual Basic Operators:
1- The simplest operators carry out arithmetic operations. These operations
in their order of precedence are:
Operation Code
Operation
^
Exponent
*,/
Multiplication and division
\
Integer division
Mod
Modulus – rest of division
-,+
Subtraction and addition
2- To Concatenate two strings, use the & symbol or the + symbol
3- There are six Comparison operators in Visual Basic.
Operation Code
Comparison
>
Greater than
<
Less than
>=
Greater than or equal to
<=
Less than or equal to
=
Equal to
< > or > <
Not equal to
4-There are three logical operators:
Operation Code
Operation
Not
Logical not
And
Logical and
Or
Logical or
Note: Logical operators follow arithmetic operators in precedence.
Examples:
Private Sub Command1_ click ( )
Picture1.Print 7\3
Picture1.Print 7 Mod 3
Picture1.Print "My"&" Name"
Picture1.Print 10/3*15/3*3/2-9/3/2*4*3
Picture1.Print 4E3-3E2/5/3E1
Picture1.Print 4E-8/2*5E8/6E16*4E14*3
Picture1.Print 4/3^3/4^2*3^4*2^4
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Ministry of Higher Education And
Scientific Research
Babylon University
College of Material Engineering
Subject: Programming in Visual Basic
Polymer Engineering Department
2015-2016
Picture1.Print
Picture1.Print
Picture1.Print
Picture1.Print
Language
Class: Second Year
Lecturer: Hussein Mohammed Salman
27^1/3-2E2^3*4E-4/4^3
(3-3^3)/((3^2+3^3)/3^5)/3^4
(14+2^5/2^4)^(1/4)+((15-5*4)/(3^2-2^3/2))
(((3^(3^3)/3^3)^(1/3)+3^4)^(1/3)* 5^2)^(1/2)
Programming Example
Stopwatch Application - Attaching Code
All that’s left to do is attach code to the application. We write code for every event a
response is needed for. In this application, there are three such events: clicking on each
of the command buttons.
Click the down arrow in the Object box and select the object named (general).
The Procedure box will show (declarations). Here, you declare three form level
variables:
Option Explicit
Dim StartTime As Variant
Dim EndTime As Variant
Dim ElapsedTime As Variant
The Option Explicit statement forces us to declare all variables. The other lines
establish StartTime, EndTime, and ElapsedTime as variables global within the form.
 Select the cmdStart object in the Object box. If the procedure that appears is not the
Click procedure, choose Click from the procedure box. Type the following code which
begins the timing procedure. Note the Sub and End Sub statements are provided for
you:
Sub cmdStart_Click ()
‘Establish and print starting time
StartTime = Now
lblStart.Caption = Format(StartTime, "hh:mm:ss")
lblEnd.Caption = ""
lblElapsed.Caption = ""
End Sub
In this procedure, once the Start Timing button is clicked, we read the current time and
This lecture allowed on: www.uobabylon.iq.edu
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Ministry of Higher Education And
Scientific Research
Babylon University
College of Material Engineering
Subject: Programming in Visual Basic
Polymer Engineering Department
2015-2016
Language
Class: Second Year
Lecturer: Hussein Mohammed Salman
print it in a label box. We also blank out the other label boxes. In the code above (and in
all code in these notes), any line beginning with a single quote (‘) is a comment. You
decide whether you want to type these lines or not. They
are not needed for proper application operation.
Now, code the cmdEnd button.
Sub cmdEnd_Click ()
‘Find the ending time, compute the elapsed time
‘Put both values in label boxes
EndTime = Now
ElapsedTime = EndTime – StartTime
lblEnd.Caption = Format(EndTime, "hh:mm:ss")
lblElapsed.Caption = Format(ElapsedTime, "hh:mm:ss")
End Sub
Here, when the End Timing button is clicked, we read the current time (End Time),
compute the elapsed time, and put both values in their corresponding label boxes.
Finally the cmdExit button:
Sub cmdExit_Click ()
End
End Sub
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Ministry of Higher Education And
Scientific Research
Babylon University
College of Material Engineering
Subject: Programming in Visual Basic
Polymer Engineering Department
2015-2016
Language
Class: Second Year
Lecturer: Hussein Mohammed Salman
Exercises:
1) Compute depending on the precedence rules (step by step) :
15/3*8/3*9/2-15/3/12*4*3
=
6/3^3/4^2*3^4*2^4
=
(3+3^3)/((3-3^3)/3^7)/3^5
=
(23+2^6/2^4)^(1/3)+((10-5*4)/(3^2-2^3/2))
=
(((3^(3^3)/3^3)^(1/3)-1)^(1/3)* 2^3)^(1/2)
=
2)
3)
4)
5)
6)
What are the naming rules of variables ?
List at least seven types of variables in VB with its suffix ?
Discuss in detail types of the variables declaration?
What are the declaration scopes in VB?
What the different between the static declaration and other declarations?
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