unit 2 vb fundamentals

PREPARED BY: EN NORZELAN BIN SALEH

ELECTRICAL ENGINEERING DEPARTMENT SULTAN HAJI AHMAD SHAH POLYTECHNIC

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List of Visual Basic data types and the range of values each one can contain.

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2.1 Data Type

Data Type Value Range

Boolean True or False

Byte 0 to 255 (unsigned)

Char A single Unicode character

Date 0:00:00 (midnight) on January 1, 0001,

through 11:59:59 p.m. on December 31,

9999

UNIT 2: VISUAL BASIC FUNDAMENTALS

Data Type Value Range Decimal 0 through +/–

79,228,162,514,264,337,593,543,950,335, with no

decimal point; +/–

7.9228162514264337593543950335, with 28 places

to the right of the decimal. Use this data type for

currency values

Double –1.79769313486231570E+308 through –

4.94065645841246544E-324 for negative values;

4.94065645841246544E-324 through

1.79769313486231570E+308 for positive values

Integer –2,147,483,648 to 2,147,483,647 (signed). This is the

same as the data type Int32.

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2.1 Data Type



Long –9, 223,372,036,854,775,808 to

9,223,372,036,854,775,807 (signed). This is

the same as data type Int64.

Object Any type can be stored in a variable of type

Object.

SByte 128 through 127 (signed)

Short –32,768 to 32,767 (signed). This is the same

as data type Int16.

4

2.1 Data Type



Single –3.4028235E+38 through –1.401298E-45 for

negative values;

1.401298E-45 through 3.4028235E+38 for

positive values

String 0 to approximately 2 billion Unicode

characters

UInteger 0 through 4,294,967,295 (unsigned)

ULong 0 through 18,446,744,073,709,551,615

(1.8...E+19) (unsigned)

UShort 0 through 65,535 (unsigned) 5

2.1 Data Type


Helpful guidelines for using data types:

To store text, use String data type. The String data type can be

used to store any valid keyboard character, including numbers

and non-alphabetic characters.

To store only the value True or False, use the Boolean data type.

To store a number that doesn't contain decimal places and is

greater than –32,768 and smaller than 32,767, use the Short data

type.

To store numbers without decimal places, but with values larger

or smaller than Short allows, use the Integer or Long (long

integer) data types.

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2.1 Data Type



To store numbers that contain decimal places, use the Single data

type. The Single data type should work for almost all values

containing decimals, except for incredibly complex mathematical

applications or need to store very large numbers. In that case, use

a Double.

To store currency amounts, use the Decimal data type.

To store a date and/or a time value, use the Date data type. When

you use the Date data type, VB recognizes common date and time

formats. Eg. if you store the value 7/22/2008, VB doesn't treat it as

a simple text string; it knows that the text represents July 22, 2008.

7

2.1 Data Type



Different data types use different amounts of memory. To

preserve system resources, it's best to use the data type that

consumes the least amount of memory and still provides the

ability to store the full range of possible values.

Eg. if you're storing only the numbers from 1 to 10, use a

Short instead of a Long.

8

2.1 Data Type


The Object data type requires special attention. If you define

a variable or array as an Object data type, you can store just

about any value you care to in it; VB determines what data

type to use when you set the variable's value.

Object data types take up more memory than the other data

types.

VB takes a little longer to perform calculations on Object data

types. Unless you have a specific reason to do so and there

are valid reasons, such as when you don't know the type of

data to be stored ahead of time don't use the Object data

type

9

2.1 Data Type


Working with Variables

A variable is an element in code that holds a value.

We might create a variable that holds the name of a user or the

user's age, for example.

Each variable (storage entity) must be created before it can be

used. The process of creating a variable is known as declaring a

variable.

Each variable is declared to hold data of a specific type, such as

text (called a string) for name or a number for age.

When we reference a variable's name in code, VB substitutes

the variable's value in place of the variable name during code

execution (at runtime the moment the variable is referenced.)

Variables can have their values changed at any time.

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Declaring Variables

The act of defining a variable is called declaring (sometimes

dimensioning), which is most commonly accomplished using

the keyword Dim (short for dimension).

Dim variablename As datatype

Example:

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Dim Number As Integer



An example of a variable declaration is

This statement creates a variable called strFirstName. This

variable is of type String, which means that it can hold any

text you choose to put into it.

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Dim strFirstName As String



We don't have to specify an initial value for a variable

It is a useful feature of VB to create a new String variable and

initialize it with a value,

eg, you could use two statements like this:

If you know the initial value of the variable at design time, you

can include it in the Dim statement, like this:

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Dim strName As String strName = “Alibaba“

Dim strName As String = “Alibaba"



Note: all data types have a default initial value.

For the string data type, the value is "Nothing"

Empty strings are written in code as "".

For numeric data types, the default value is 0;

the output of the following statements would be 2:

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Dim sngMyValue As Single Debug.WriteLine (sngMyValue + 2)



Passing Values to a Variable

The syntax of assigning a literal value such as 6 or “six") to a

variable depends on the variable's data type.

For strings, you must pass the value in quotation marks, like

this:

For Date values, you enclose the value in # symbols, like this:

For numeric values, you don't enclose the value in anything:

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strCollegeName = “POLISAS"

dteBirthDate = #7/22/1969#

intAge = 42



Using Variables in Expressions

Variables can be used anywhere an expression is expected.

Eg. The arithmetic functions, operate on expressions. You

could add two literal numbers and store the result in a

variable like this:

In addition, you could replace either or both literal numbers

with numeric variables or constants, as shown here:

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intSum = 2 + 5

intSum = intFirstValue + 5 intSum = 2 + intSecondValue intSum = intFirstValue + intSecondValue



Variables are a fantastic way to store values during code

execution, and you'll use variables all the time from

performing decisions and creating loops to using them as a

temporary place to stick a value.

Remember to use a constant when you know the value at

design time and the value won't change.

When you don't know the value ahead of time or the value

might change, use a variable with a data type appropriate to

the variable's function

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Variable Scope

Constants, variables, and arrays are useful ways to store and

retrieve data in VB code.

Hardly a program is written that doesn't use at least one of

these elements. To properly use them, however, it's critical

that you understand scope.

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Variable Scope

Code is written in procedures and procedures are stored in

modules.

Scope refers to the level at which a constant, variable, array,

or procedure can be "seen" in code.

For a constant or variable, scope can be one of the following:

Block level

Procedure level (local)

Module level

Global (also called namespace scope)

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Variable Scope

1. Block Scope (or Structure Scope)

- a variable dimensioned within a structure, is given a

structure scope.

- Structures are coding constructs that consist of two

statements, eg. If..Then statement, Do..Loop Statement

If expression Then

statements to execute when expression is True

End If

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Variable Scope


Do

statements to execute in the loop

Loop

- If a variable is declared within a structure, the variable's

scope is confined to the structure; the variable isn't created

until the Dim statement occurs, and it's destroyed when the

structure completes.

- If a variable is needed only within a structure, consider

declaring it in the structure to give it block scope

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Variable Scope


- Consider the following example:

- By placing the Dim statement within the If structure, you ensure

that the variable is created only if it's needed.

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If blnCreateLoop Then Dim intCounter As Integer For intCounter = 1 to 100 ' Do something Next intCounter End If



Variable Scope

2. Procedure-Level (Local) Scope.

A constant or variable declared within a procedure, has

procedure-level or local scope.

Most of the variables created will have procedure scope.

A local constant or variable can be referenced within the

same procedure, but it isn't visible to other procedures.

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Variable Scope

2. Procedure-Level (Local) Scope.

If a local constant or variable is referenced from a procedure

other than the one in which it's defined, VB returns a compile

error; to the procedure making the reference, the variable or

constant doesn't exist.

It's a best practice to declare all local variables at the top of a

procedure, but VB doesn't care where we place the Dim

statements within the procedure.

Note that if you place a Dim statement within a structure, the

corresponding variable will have block scope, not local scope.

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Variable Scope

3. Module-Level Scope

Constant or variable with module-level scope, can be viewed by

all procedures within the module containing the declaration.

the constant or variable doesn't exist to procedures in all other

modules.

To create a constant or variable with module-level scope, the

declaration is placed within a module but not within a procedure.

There is a Declarations section at the top of each module.

Use module-level scope when many procedures must share the

same constant or variable and when passing the value as a

parameter is not a workable solution.

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Variable Scope

4. Global (Namespace) Scope

A global scope (or namespace scope) constant or variable can be seen

and referenced from any procedure, regardless of the module in which

the procedure exists.

One common use of a global variable is storing a reference to a

database connection so that all code that needs access to the database

can do so via the variable.

Creating global constants and variables is similar to declaring module-

level constants and variables.

Global constants and variables must be declared in a module's

Declarations section, just like module level constants and variables.

The difference between a module-level declaration and a global-level

declaration is the use of the keyword Public.

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Variable Scope


To declare a global constant, begin the constant declaration

with the word Public:

Public Const MyConstant As Integer = 1

To dimension a variable as a global variable, replace the

keyword Dim or Private with the word Public:

Public strMyVariable as String

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Variable Scope


To create a constant or variable of global scope, you must

declare the constant or variable in a standard module, not a

class-based module.

We can't have two variables of the same name in the same

scope, but we can use the same variable name for variables

with different scope.

when referencing the variable name in the procedure

containing the local variable, VB would use the local variable.

When accessing the variable from another procedure, the

local variable is invisible, so the code would reference the

global variable

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Understanding Constants

a constant represent an identifier having a specific value at

design time, and that value never changes throughout the life

of your program.

Constants offer the following benefits:

1. They eliminate or reduce data-entry problems

2. Code is easier to update

3. Code is easier to read

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Constant definitions have the following syntax:

Const name As datatype = value

Example:

Statement to define a constant to hold the value of pi

Const pi As Single = 3.14159265358979

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After a constant is defined, we can use its name in code in

place of its value.

For example, to calculate the value of Circle_area, we use:

Using the constant is much easier and less prone to error

than typing this:

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Circle_area=pi*radius^2

Circle_area=3.14159265358979 * radius^2


Naming Convention

To make code more self-documenting and to reduce the

chance of programming errors, you need an easy way to

determine the exact data type of a variable or the exact type

of a referenced control in VB code.

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Naming Convention

1. Using Prefixes to Denote Data Type.

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Data Type Prefix Sample Value

Boolean bln blnLoggedIn

Byte byt bytAge

Char chr chrQuantity

Date dte dteBirthday

Decimal dbc decSalary

Double dbl dblCalculatedResult

Integer int intLoopCounter

Long lng lngCustomerID

Object obj objWord

Short sho shoTotalParts

Single sng sngMortgageRate

String str strFirstName


Naming Convention

1. Denoting Scope Using Variable Prefixes

In particularly large applications, a scope designator is a

necessity.

Visual Basic doesn't care whether you use prefixes, but

consistently using prefixes benefits you as well as others who

have to review your code

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Prefix Description Example

g_ Global g_strSavePath

m_ Module-level m_blnDataChanged

s_ Static variable s_blnInHere

No prefix Nonstatic variable, local to procedure

Prefix Description Example


Related Links:

http://msdn.microsoft.com/en-

us/library/gg145045(v=VS.100).aspx

.Net Framework Class Library contains many predefined classes that

are grouped into namespaces which uses Import statement to

specify the namespaces used in a program

Example:

Import System.Windows.Forms

The declaration above will enable the program to use classes in this

namespace, such as class MessageBox.

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http://msdn.microsoft.com/en-us/library/gg145045(v=VS.100).aspx



Related Links: http://msdn.microsoft.com/en-us/library/zdf6yhx5.aspx

http://msdn.microsoft.com/en-us/library/system.console.readline.aspx

http://msdn.microsoft.com/en-us/library/system.console.aspx

http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx#DFormatString

ReadLine : Reads the next line of characters from the

standard input stream.

WriteLine : Writes the current line terminator to the

standard output stream.

Write : Writes the text representation of the specified value

or values to the standard output stream.

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http://msdn.microsoft.com/en-us/library/zdf6yhx5.aspx









http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx



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Format

specifier

Name Description Examples

"C" or "c" Currency Result: A currency value.

Supported by: All numeric types.

Precision specifier: Number of decimal digits.

Default precision specifier: Defined by

System.Globalization.NumberFormatInfo.

More information: The Currency ("C") Format Specifier.

123.456 ("C", en-US) -> $123.46

123.456 ("C", fr-FR) -> 123,46 €

123.456 ("C", ja-JP) -> ¥123

-123.456 ("C3", en-US) -> ($123.456)

-123.456 ("C3", fr-FR) -> -123,456 €

-123.456 ("C3", ja-JP) -> -¥123.456

"D" or "d" Decimal Result: Integer digits with optional negative sign.

Supported by: Integral types only.

Precision specifier: Minimum number of digits.

Default precision specifier: Minimum number of digits required.

More information: The Decimal("D") Format Specifier.

1234 ("D") -> 1234

-1234 ("D6") -> -001234

"E" or "e" Exponential

(scientific)

Result: Exponential notation.



Default precision specifier: 6.

More information: The Exponential ("E") Format Specifier.

1052.0329112756 ("E", en-US) ->

1.052033E+003

1052.0329112756 ("e", fr-FR) ->

1,052033e+003

-1052.0329112756 ("e2", en-US) -> -

1.05e+003

-1052.0329112756 ("E2", fr_FR) -> -

1,05E+003

http://msdn.microsoft.com/en-us/library/system.globalization.numberformatinfo.aspx




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Format

specifier


"F" or "f" Fixed-point Result: Integral and decimal digits with optional negative sign.





More information: The Fixed-Point ("F") Format Specifier.

1234.567 ("F", en-US) -> 1234.57

1234.567 ("F", de-DE) -> 1234,57

1234 ("F1", en-US) -> 1234.0

1234 ("F1", de-DE) -> 1234,0

-1234.56 ("F4", en-US) -> -1234.5600

-1234.56 ("F4", de-DE) -> -1234,5600

"G" or "g" General Result: The most compact of either fixed-point or scientific

notation.


Precision specifier: Number of significant digits.

Default precision specifier: Depends on numeric type.

More information: The General ("G") Format Specifier.

-123.456 ("G", en-US) -> -123.456

123.456 ("G", sv-SE) -> -123,456

123.4546 ("G4", en-US) -> 123.5

123.4546 ("G4", sv-SE) -> 123,5

-1.234567890e-25 ("G", en-US) -> -

1.23456789E-25

-1.234567890e-25 ("G", sv-SE) -> -

1,23456789E-25

"N" or "n" Number Result: Integral and decimal digits, group separators, and a

decimal separator with optional negative sign.


Precision specifier: Desired number of decimal places.



More information: The Numeric ("N") Format Specifier.

1234.567 ("N", en-US) -> 1,234.57

1234.567 ("N", ru-RU) -> 1 234,57

1234 ("N", en-US) -> 1,234.0

1234 ("N", ru-RU) -> 1 234,0

-1234.56 ("N", en-US) -> -1,234.560

-1234.56 ("N", ru-RU) -> -1 234,560








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Format

specifier


"P" or "p" Percent Result: Number multiplied by 100 and displayed with a percent

symbol.


Precision specifier: Desired number of decimal places.



More information: The Percent ("P") Format Specifier.

1 ("P", en-US) -> 100.00 %

1 ("P", fr-FR) -> 100,00 %

-0.39678 ("P1", en-US) -> -39.7 %

-0.39678 ("P1", fr-FR) -> -39,7 %

"R" or "r" Round-trip Result: A string that can round-trip to an identical number.

Supported by: Single, Double, and BigInteger.

Precision specifier: Ignored.

More information: The Round-trip ("R") Format Specifier.

123456789.12345678 ("R") ->

123456789.12345678

-1234567890.12345678 ("R") -> -

1234567890.1234567

"X" or "x" Hexadecimal Result: A hexadecimal string.

Supported by: Integral types only.

Precision specifier: Number of digits in the result string.

More information: The HexaDecimal ("X") Format Specifier.

255 ("X") -> FF

-1 ("x") -> ff

255 ("x4") -> 00ff

-1 ("X4") -> 00FF

Refer Unit2 eg1.vbp




http://msdn.microsoft.com/en-us/library/system.single.aspx

http://msdn.microsoft.com/en-us/library/system.double.aspx

http://msdn.microsoft.com/en-us/library/system.numerics.biginteger.aspx









Syntax Represents

Literals a = 5;

Integer Numerals 1776707-273

75 ‘ decimal

&O43 ‘ octal

&HFF3 ‘hexadecimal

"Z"C ‘ char

vbCR a carriage-return character for print and display

functions.

vbTab a tab character for print and display functions.

vbCrLf a carriage-return character combined with a linefeed

character for print and display functions.

vbNullString a zero-length string for print and display functions,

and for calling external procedures.

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If used, the Option Explicit statement must appear in a file

before any other source code statements.

When Option Explicit appears in a file, you must explicitly

declare all variables using the Dim or ReDim statements. If

you attempt to use an undeclared variable name, an error

occurs at compile time.

Use Option Explicit to avoid incorrectly typing the name of

an existing variable or to avoid confusion in code where the

scope of the variable is not clear.

If the Option Explicit statement is not used, all undeclared

variables are of Object type.

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Restricts implicit data type conversions to only widening

conversions.

If used, the Option Strict statement must appear in a file

before any other source code statements.

VB allows conversions of many data types to other data

types. Data loss can occur when the value of one data type is

converted to a data type with less precision or smaller

capacity. A run-time error occurs if such a narrowing

conversion fails.

Option Strict ensures compile-time notification of these

narrowing conversions so they can be avoided.

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An operation is at least one value combined with a symbol to

produce a new value.

A more complex operation can involve more than one value

and possibly more than one symbol.

A value involved in an operation is called an operand.

A symbol involved in an operation is called an operator.

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Types of operators:

Arithmetic operators

Boolean operators

Relational operators

Bitwise operators

unary operators. - Operators that work with only one

operand are called

binary operators - operators who work with two operands

are called

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Symbol Syntax Example

^

result = number^exponent Dim MyValue

MyValue = 2 ^ 2 'Returns 4.

MyValue = 3 ^ 3 ^ 3 'Returns 19683.

MyValue = (-5) ^ 3 'Returns -125.

*

multiply two numbers.

result = number1*number2

Dim MyValue

MyValue = 2 * 2 ' Returns 4.

MyValue = 459.35 * 334.90'Returns

153836.315.

/

divide two numbers and return a

floating-point result.

result = number1/number2

Dim MyValue

MyValue = 10 / 4 ' Returns 2.5.

MyValue = 10 / 3 ' Returns 3.333333.

\

divide two numbers and return an

integer result.

result = number1\number2

Dim MyValue

MyValue = 11 \ 4 ' Returns 2.

MyValue = 9 \ 3 ' Returns 3.

MyValue = 100 \ 3 ' Returns 33. 45

1. Arithmetic Operators



Mod

divide two numbers and

return only the remainder

result = number1 Mod

number2.

Dim MyResult

MyResult = 10 Mod 5 ' Returns 0.

MyResult = 10 Mod 3 ' Returns 1.

MyResult = 12 Mod 4.3 ' Returns 0.

MyResult = 12.6 Mod 5 ' Returns 3.

+

sum two numbers.

result =

expression1+expression2

Dim MyNumber, Var1, Var2

MyNumber = 2 + 2 ' Returns 4.

MyNumber = 4257.04 + 98112 ' Returns 102369.04.

Var1 = "34": Var2 = 6 ' Initialize mixed variables.

MyNumber = Var1 + Var2 ' Returns 40.

Var1 = "34": Var2 = "6" ' Initialize variables with strings.

MyNumber = Var1 + Var2' Returns "346" (string

concatenation).

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-

Used to find the difference

between two numbers or to

indicate the negative value

of a numeric expression.

result = number1–number2

–number

Dim MyResult

MyResult = 4 - 2 ' Returns 2.

MyResult = 459.35 - 334.90 ' Returns 124.45.

&

Used to force string

concatenation of two

expressions.

result = expression1 &

expression2

Dim MyStr

MyStr = "Hello" & " World" ' Returns "Hello World".

MyStr = "Check " & 123 & " Check" ' Returns

"Check 123 Check".

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ms-help://MS.MSACCESS.DEV.12.1033/MSACCESS.DEV/content/HV01200929.htm


Symbol Syntax Meaning

= X = Y X is equal to Y

<> X <> Y X is not equal to Y

> X > Y X is greater than Y

< X < Y X is less than Y

>= X >= Y X is greater than or equal to Y

<= X <= Y X is Less than or equal to Y

Like result = string Like pattern Used to compare two strings.

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2. Equality and Relational Operators

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3. Logical (Boolean) operators Symbol Syntax Example

Not

Used to perform logical negation on an expression. result = Not expression

Dim A, B, C, D, MyCheck A = 10: B = 8: C = 6: D = Null ' Initialize variables. MyCheck = Not(A > B) 'Returns False. MyCheck = Not(B > A) 'Returns True. MyCheck = Not(C > D)' Returns Null. MyCheck = Not A 'Returns -11 (bitwise comparison).

And

Used to perform a logical conjunction on two expressions. result = expression1 And expression2

Dim A, B, C, D, MyCheck A = 10: B = 8: C = 6: D = Null ' Initialize variables. MyCheck = A > B And B > C ' Returns True. MyCheck = B > A And B > C ' Returns False. MyCheck = A > B And B > D ' Returns Null. MyCheck = A And B ' Returns 8 (bitwise comparison).

Or

Used to perform a logical conjunction on two expressions result = expression1 Or expression2

Dim A, B, C, D, MyCheck A = 10: B = 8: C = 6: D = Null ' Initialize variables. MyCheck = A > B Or B > C ' Returns True. MyCheck = B > A Or B > C ' Returns True. MyCheck = A > B Or B > D ' Returns True. MyCheck = B > D Or B > A ' Returns Null. MyCheck = A Or B ' Returns 10 (bitwise comparison).




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3. Logical (Boolean) operators


Xor

Used to perform a logical exclusion on two expressions. [result =] expression1 Xor expression2

Dim A, B, C, D, MyCheck A = 10: B = 8: C = 6: D = Null ' Initialize variables. MyCheck = A > B Xor B > C ' Returns False. MyCheck = B > A Xor B > C ' Returns True. MyCheck = B > A Xor C > B ' Returns False. MyCheck = B > D Xor A > B ' Returns Null. MyCheck = A Xor B ' Returns 2 (bitwise comparison).

Eqv

Used to perform a logical equivalence on two expressions. result = expression1 Eqv expression2

Dim A, B, C, D, MyCheck A = 10: B = 8: C = 6: D = Null ' Initialize variables. MyCheck = A > B Eqv B > C ' Returns True. MyCheck = B > A Eqv B > C ' Returns False. MyCheck = A > B Eqv B > D ' Returns Null. MyCheck = A Eqv B ' Returns -3 (bitwise comparison).

Imp

Used to perform a logical implication on two expressions result = expression1 Imp expression2

Dim A, B, C, D, MyCheck A = 10: B = 8: C = 6: D = Null ' Initialize variables. MyCheck = A > B Imp B > C ' Returns True. MyCheck = A > B Imp C > B ' Returns False. MyCheck = B > A Imp C > B ' Returns True. MyCheck = B > A Imp C > D ' Returns True. MyCheck = C > D Imp B > A ' Returns Null. MyCheck = B Imp A ' Returns -1 (bitwise comparison).




Symbol Function Example

<< Performs an arithmetic left shift on a bit pattern.

Dim pattern As Short = 192' The bit pattern is 0000 0000 1100 0000.Dim result As Shortresult = pattern << 4 pattern is 192 0000 0000 1100 0000 result is 3072 0000 1100 0000 0000

>> Performs an arithmetic right shift on a bit pattern.

Dim pattern As Short = 2560' The bit pattern is 0000 1010 0000 0000.Dim result As Shortresult2 = pattern >> 4 pattern is 2560 0000 1010 0000 0000 result is 160 0000 0000 1010 0000

>>=

Performs an arithmetic right shift on the value of a variable or property and assigns the result back to the variable or property

<<=

Performs an arithmetic left shift on the value of a variable or property and assigns the result back to the variable or property.

51


4. Bitwise Operators

Compound

assignment operator

Sample expression Explanation

+= c+=7 c=c+7

-= c-=3 c=c-3

*= c*=4 c=c*4

/= c/=2 c=c/2

\= c\=3 c=c\3

^= c^=2 c=c^2

&= d&=”llo” d=d&”llo”

<<= c<<=1 c=c<<1

>>= c>>= c=c>>1

52


5. Compound Assignment Operators

In VB we have two operators for string concatenation. The plus

+ operator and the & ampersand operator.

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Option Strict On

Module Example

Sub Main()

Console.WriteLine(“Politeknik " & “Sultan " & “Haji Ahmad Shah")

Console.WriteLine(“Politeknik " + “Sultan " + “Haji Ahmad Shah")

End Sub

End Module


6. Concatenating Strings operators

Dim strA As String Dim strB As String Dim intA As Short Dim dblB As Decimal strA = "POLITEKNIK " strB = "SULTAN HAJI AHMAD SHAH " intA = 1234 dblB = 1234.567 Console.WriteLine(strA & strB) Console.WriteLine(strA + strB) Console.WriteLine(intA & dblB) Console.WriteLine(intA + dblB)

54


6. Concatenating Strings

Operator Operation

1 ^ Exponentiation

2 +,- Sign operations

3 *,/ Multiplication and Division

4 \ Integer division

5 Mod Modulus

6 +,- Addition and Subtraction

7 & concatenation

8 <<, >> Bitwise

9 =, <>, <, <=, >=, Like, Is Relational

10 Not Logical NOT

11 And, AndAlso Logical AND

12 Or, OrElse Logical inclusive OR

13 Xor Logical exclusive OR

14 =, +=, -=, *=, /=, \=, ^=, &= Assignment

55


Hierarchy of Operators Precedence

Decision-making or Selection Control Structures are coding

structures that enable you to execute or omit code based on

a condition, such as the value of a variable.

VB includes two constructs that enable you to make any type

of branching decision you can think of:

If...Then...Else and Select Case.

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The If Statement

1. If..Then statement

Syntax:

If expression Then

... ' code to execute when expression is True.

End If

If the expression evaluates to True, the code placed

between the If statement and the End If statement

gets executed. If the expression evaluates to False,

Visual Basic jumps to the End If statement and

continues execution from there, bypassing all the

code between the If and End If statements.

57


The If Statement

Example:

58

If IsNumeric(txtInput.Text) Then MessageBox.Show("The text is a number.") End If


The If Statement

Examples:

Private Sub Button1_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles Button1.Click

If RadioButton1.Checked = True Then

MsgBox("RadioButton1 selected")

End If



End If

End Sub

59


The If Statement

2. Else Statement

to execute some code when expression evaluates to False,

include an Else statement between If and End If:

Syntax:

If expression Then

... ' code to execute when expression is True.

Else

... ' code to execute when expression is False.

End If

60


The If Statement

Example:

If IsNumeric(txtInput.Text) Then

MessageBox.Show("The text is a number.")

Else

MessageBox.Show("The text is not a number.")

End If

61


The If Statement

3. ElseIf Statement

The ElseIf statement allows you to evaluate a second

expression when an If...Then statement equates to False.

Syntax:

If expression Then

...

ElseIf expression2 Then

...

End If

62


Example:



ElseIf RadioButton2.Checked = True Then


End If

63


The If Statement

3. Nested If..Then

Syntax:

If expression Then

...

Else

If expression2 Then

...

End If

End If

64


Example:


If CheckBox1.Checked = True Then

MsgBox("RadioButton1 and CheckBox1 selected")

Else : MsgBox("radioButton1 and ChechBox2 selected")

End If

ElseIf RadioButton2.Checked = True Then

If CheckBox1.Checked = True Then

MsgBox("RadioButton2 and CheckBox1 selected")

Else : MsgBox("radioButton2 and ChechBox2 selected")

End If

End If

65


The Select case statement

Syntax:

Select Case expression

Case value1

...

Case value2

...

Case value3

...

Case Else

...

End Select

66

Case Else is used to define code that

executes only when expression doesn't

evaluate to any of the values in the

Case statements. Use of Case Else is

optional.


The Select case statement for Multiple Selections

The Select Case statement enables you to create some

difficult expression comparisons.

Eg. specify multiple comparisons in a single Case statement

by separating the comparisons with a (,).

67



Examples:

68

Select Case lngAge Case 1 To 7 ' Code placed here executes if lngAge is 1, 7 or any number in between. End Select

Select Case strName Case "Hartman" To "White" ' Code placed here executes if the string is Hartman, White, ' or if the string falls alphabetically between these two names. End Select



Examples:

69

Select Case lngAge Case < 10 ... Case 10 To 17 ... Case 18 To 20 ... Case Else ... End Select


The Select case statement Dim Number

Number = 8 ' Initialize variable.

Select Case Number ' Evaluate Number.

Case 1 To 5 ' Number between 1 and 5, inclusive.

Console.WriteLine("Between 1 and 5")

Case 6, 7, 8 ' Number between 6 and 8.

Console.WriteLine("Between 6 and 8")

Case 9 To 10 ' Number is 9 or 10.

Console.WriteLine("Greater than 8")

Case Else ' Other values.

Console.WriteLine("Not between 1 and 10")

End Select

70


1. For...Next Loop

Syntax:

For countervariable = start To end [Step step]

... [statements to execute in loop]

[Exit For]

... [statements to execute in loop]

Next [countervariable]

71


1. For...Next Loop

Components of a for loop:

72

Part Description

countervariable A previously declared variable of a numeric data type (Integer, Long,

and so on). This variable is incremented each time the loop occurs.

start The number you want to start counting from.

end

The number you want to count to. When countervariable reaches the

end number, the statements within the For...Next loop are executed a

final time, and execution continues with the line following the Next

statement.

step

The amount by which you want countervariable incremented each time

the loop is performed. step is an optional parameter; if you omit it,

countervariable is incremented by 1.

Exit For A statement that can be used to exit the loop at any time. When Exit

For is encountered, execution jumps to the statement following Next.


1. For...Next Loop

Examples:

73

Dim intCounter As Integer

For intCounter = 1 To 10

Console.WriteLine(intCounter)

Next intCounter




Next

Note: Both examples will produce the same results.


1. For...Next Loop

Example:

74


Dim intSecondCounter As Integer


For intSecondCounter = 1 To 5

Console.WriteLine(intSecondCounter)

Next intSecondCounter

Next intCounter


1. For...Next Loop

Using step

Step is used in a For...Next statement to

designate the value by which to increment the

counter variable each time the loop occurs.

Example:

75


For intCounter = 1 To 100 Step 4


Next intCounter


2. Do . . . Loop

Syntax:

Do

[Statements]

Loop

You could start a For...Next loop specifying an upper limit

that you know is larger than the number of loops needed,

check for a terminating condition within the loop, and exit

the loop using an Exit For statement when the condition is

met.

76


2. Do . . . Loop

Example:

Dim counter As Integer = 10

Do

Console.WriteLine(counter)

Loop

Caution:

This is an infinite loop. Why????

77


2. Do . . . Loop

More complete Syntax:

Do

[Statements]

If expression Then Exit Do

Loop

In this code, the loop would execute until

expression evaluates to True.

78


2. Do..Loop

Example:


Do


counter += 2

If counter > 10 Then Exit Do

Loop

79

Loop Control Structure


2. Do..Loop

Flowchart:

80

If Counter

>10

Start or initialize Counter =1

Yes

No

Increment (counter+=2)

Display value of counter



2. Do . . . Loop

More Syntax:

Do While expression

[Statements]

Loop

As long as expression evaluates to True, this loop

continues to occur. If expression evaluates to

False when the loop first starts, the code between

the Do While and Loop statements doesn't

execute not even once

81



2. Do . . . Loop

Example:


Do While (counter < 10)


counter += 2

Loop

82


2. Do . . . Loop

More Syntax:

Do Until expression

[Statements]

Loop

the loop executes repeatedly until expression

evaluates to True

83


2. Do . . . Loop

Example:


Do Until (counter > 10)


counter += 2

Loop

84


2. Do..Loop

Flowchart:

85

If Counter

>10


Yes

No




2. Do . . . Loop

More Syntax:

Do

[Statements]

Loop While expression

This loop executes as long as expression evaluates to True

The difference between the Do...While and Do...Loop While

loops:

Code between the Do and the Loop While statements always

executes at least once; expression isn't evaluated until the

loop has completed its first cycle. Again, such a loop always

executes at least once, regardless of the value of expression.

86



2. Do . . . Loop

Example:


Do


counter += 2

Loop While (counter < 10)

87



2. Do . . . Loop

More Syntax:

Do

[Statements]

Loop Until expression

This loop executes until expression evaluates to

True. However, the code within this loop always

executes at least once; expression isn't evaluated

until the loop completes its first cycle.

88


2. Do . . . Loop

Example:


Do


counter += 2

Loop Until (counter > 10)

89


3. While...End While Loop Statement

Syntax

While condition

[statements]

End While

90



Example:

Dim Counter As Short = 1

While Counter < 10

Counter += 2

Console.WriteLine(Counter)

End While

91



Flowchart

92

If Counter

<10


Yes

No




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