Procedures functions structures in VB.Net

Visual Programming with
Visual Basic .NET
Procedures, Functions and Structures

Procedures
 Procedure
 A block of statements enclosed by a declaration
statement and an End statement
 Invoked from some other place in the code
 When finished the execution, returns control to
the code that invoked it

 Provide a way to break larger complex programs
into smaller and simple logical units – Divide and
conquer
 Make code easier to read, understand and debug
 Enable code reusability
 Can be a sub procedure, function procedure or an
event procedure
2

Example
Boss
Worker1

Worker4

Worker2

Worker5

Worker3

Click Here for
more details

 Boss assigns work to the workers
 A worker may assign part of his work to a
subordinate
 Once the given job is completed, boss can continue
with his work
 How the worker does the work is not important here
3

Sub Procedures
 Sub procedure
 A series of statements enclosed by the Sub and
End Sub statements
 Performs actions but does not return a value to the
calling code
 Can take arguments that are passed by the calling
code
 Can define in modules, classes and structures

4

Declaration of Sub Procedures
 Declaration syntax
[AccessSpecifier] Sub Identifier([ParameterList])
[Statements]
End Sub

 AccessSpecifier could be Public, Protected, Friend,
or Private
 If omitted, it is Public by default

 Identifier specifies the identifier of the procedure
 ParameterList is a comma-separated list of
parameters
 Exit Sub statement can be used to exit immediately
from a Sub procedure

5

Declaration of Sub Procedures
 Declaration syntax for Parameters

[ByVal|

ByRef] Identifier As DataType

or

Optional
[ByVal|ByRef] Identifier As DataType = _
DefaultValue

 ByVal or ByRef specifies the argument passing
mechanism
 If omitted, it is assumed ByVal by default

 Optional indicates whether the argument is optional
 If so, a default value must be declared for use in
case, if the calling code does not supply an argument
 Parameters following a parameter corresponding to
an optional argument must also be optional

6

Argument Passing Mechanisms
 Argument can be passed to a procedure by value
or by reference by specifying ByVal or ByRef
keywords, respectively
 Passing by value means the procedure can not
modify the contents of arguments in calling code
 Passing by reference allows the procedure to
modify the contents of arguments in calling code
 Non-variable arguments in calling code are never
modified, even if they are passed by reference

7

Argument Passing Mechanisms
 Passing arguments ByVal
 Protects arguments from being changed by the
procedure
 Affects to the performance due to the copying of
the entire data content of arguments to their
corresponding parameters

 Passing arguments ByRef
 Enables the procedure to return values to the
calling code through the arguments
 Reduces the overhead of copying the arguments to
their corresponding parameters but can lead to an
accidental corruption of caller’s data

8

Function Procedures
 Function procedure
 A series of statements enclosed by the Function
and End Function statements
 Similar to a Sub procedure, but can return a value
to the calling program
 Can take arguments that are passed by the calling
code
 Can define in modules, classes and structures

9

Declaration of Function Procedures
[AccessSpecifier] Function _
Identifier([ParameterList]) [As DataType]
[Statements]
Return ReturnExpression
End Function

or Private
 If omitted, it is Public by default

 Identifier specifies the identifier of the function
 ParameterList is a comma-separated list of
parameters
 DataType is the data type of ReturnExpression

10

Structures
 Allows to create User Defined Data Types.
 Once declared, a structure becomes a composite
data type and can declare variables of that
composite type
 Like classes, can have data members and member
functions
 Unlike classes
 Structures are value type, not reference type
 Can not inherit from another structure. So suitable
for objects which are more unlikely to extend
 All members are Public by default

11

Declaration of Structures
[AccessSpecifier] Structure Identifier
MemberVariableDeclarations
[MemberFunctionDeclarations]
End Structure

 Can only be declared at module or class level
 AccessSpecifier could be Public, Protected, Friend, or
Private
 If omitted, it is Friend by default

 Members could be Dim, Public, Friend, or Private, but
not Protected
 Must contain at least one member variable
 Member variables can’t be initialized at the declaration
 Array members should be declared without the size.
Have to use ReDim to resize.
12

Variables of Composite Data Types
 Variables of composite data types can be declared
with the data types defined as the structures
Dim Identifier As CompositeDataType






Can be used at method, class and module levels
Identifier specifies the identifier of the variable
CompositeDataType stands for structure defined
Possible to declare several variables of same type
or of different types in one statement

13

Using Composite Variables
 Members of a composite variable can be accessed
with the period character
 Syntax
CompositeVariable.Member

 To set a value to a member variable
CompositeVariable.MemberVariable = Expression

 To get the value in member variable
CompositeVariable.MemberVariable

 To call a member function
CompositeVariable.MemberFunction([ArgumentList])

14

Methods of Math Class
 Function procedures (Methods) contained in class
“Math”
 Performs mathematical operations and returns a
value

Method

Description

Example

Abs(x)

Returns the absolute value of x

Abs(-23.5) is 23.5

Ceiling(x)

Ceiling(9.2) is 10.0

Cos(x)

Rounds x to the smallest integer
not less than x
Returns trigonometric cosine of x

Exp(x)

Returns the exponential e

x

Cos(0.0) is 1.0
Exp(1.0) is
2.728281828459
05 approximately
15

Methods of Math Class
Method

Description

Example

Max(x,y)

Rounds x to the largest integer not
greater than x
Returns the natural logarithm of x
(base e)
Returns the maximum value of x & y

Min(x,y)

Returns the minimum value of x & y

Pow(x,y)

Calculates x raised to power y

Sin(x)

Returns the trigonometric sine of x

Pow(2.0,7.0) is
128
Sin(0.0) is 0.0

Sqrt(x)

Returns the square root of x

Sqrt(9.0) is 3.0

Tan(x)

Returns the trigonometric tangent
of x

Tan(0.0) is 0.0

Round(x)
Round(X, dp)

Rounds x. If given the # of decimal
places, it rounds to that decimal places

Round(2.3) is 2

Floor(x)
Log(x)

Floor(9.2) is 9.0
Log(2.718281828459
05) is 1.0 app.

Max (5,8) is 8
Min(5,8) is 5

16

Random Number Generation
 What is a random number?
Dim RandomObject as Random = new Random()
Dim RandNum as Integer = RandomObject.Next()

 This generates a positive Integer from 0 to
Int32.Maxvalue i.e. 2,147,483,647
 We can give the range to produce random
numbers.
Value = randomobject.Next(1,7)

 This returns a value between 1-6
 If passed only one parameter, it will return a
value from 0 to the passed value but excluding
that value.
 Rnd() returns a random number between 0 and 1
17

Methods of String Class
 Two types

 Shared Methods –

No Need to mention the instance name

If Compare(strA,strB)

 Non shared Methods -

>

0 Then

…

Needs to mention the instance name

If myString.EndsWith(“ed”) Then
Method

…

Description

EndsWith(x)

Checks whether the string instance ends with x

Equals(x)

Checks whether the string instance equals x

Indexof(X)

Returns the index where strinx x is found in the given string

Insert(startindex, X)

X will be inserted into the given string starting at the given position

Remove(stIndx, NofChrs)

Removes the given # of characters starting at the given position

Replace(oldstr, newstr)

Replace the old string part with the new one

StartsWith(x)

Checks whether the string instance starts with x

ToLower(), ToUpper()

Converts to Lower Case or Upper Case

Trim(), TrimEnd(),
TrimStart()

Remove spaces from both sides, from start or from end
18

Functions to Determine Data Type

Method

Description

IsArray(Variable Name)

Checks whether the variable is an array

IsDate(Expression)

Checks whether the expression is a valid data or time value

IsNumeric(Expression)

Checks whether the expression evaluates to a numeric value

IsObject(variable Name)

Checks whether the variable is an object

Is Nothing

Checks whether the object is set to nothing
If objMyObject Is Nothing Then …

TypeOf

Checks the type of an object variable
If TypeOf txtName is TextBox Then …

TypeName(Variable
Name)

Returns the data type of a non object type variable

19

Date / Time Functions
 When a Date type variable is declared, CLR uses
the DateTime structure, which has an extensible
list of properties and methods
 Now() and Today() are two shared members
Ex.
datToday = Today()
 Non shared members could be used with the
instance name of the DateTime structure

20

Date / Time Functions
Method

Description

Date

Date Component

Day

Integer day of month (1-31)

DayOfWeek

Integer day of week ( 0 = Sunday)

DayOfYear

Integer day of year ( 1-366)

Hour

Integer hour (0-23)

Minute

Integer minute (0-59)

Second

Integer second (0-59)

Month

Integer month ( 1 = January )

Year

Year component

ToLongDateString

Date formatted as long date

ToLongTimeString

Date formatted as long time

ToShortDateString

Date formatted as short date

ToShortTimeString

Date formatted as short time

21

In Built String Functions
Function
InStr
LCase
Left
Len
LTrim
Mid
StrReverse
Right
RTrim
Str
Trim
UCase

Description
Finds the starting position of a substring
within a string
Converts a string to lower case
Finds or removes a specified number of
characters from the beginning of a string
Gives the length of a string
Removes spaces from the beginning of a
string
Finds or removes characters from a
string
Reverses the strings
Finds or removes a specified number of
characters from the end of a string
Removes spaces from the end of a string
Returns the string equivalent of a
number
Trims spaces from both the beginning
and end of a string
Converts a string to upper case

Example
InStr(“My mother”, “mo”) = 4
LCase(“UPPER Case”) = upper case
Left(“Kelaniya”, 6) = “Kelani”
Len(“Hello”) = 5
LTrim(“ Hello “) = “Hello “
Mid(“microsoft”,3,4) = “cros”
strReverse(“Kelaniya”) = “ayinaleK”
Right(“Kelaniya”, 6) = “laniya”
RTrim(“ Hello “) = “ Hello“
Str(12345) = “12345”
Trim(“ Hello “) = “Hello“
UCase(“lower Case”) = “UPPER CASE”

22

Recursive Procedures
 A procedure calls itself for a repetitive task
 Ex. Calculating the Factorial Value

 Any problem that can be solved recursively could
be solved iteratively
 But recursions more naturally mirrors some
problems, hence easy to understand and debug
23

Classes
 Standard programming unit in OOP
 Encapsulate data members and member functions
into one package
 Enable inheritance and polymorphism
 Act as a template for creating objects

24

Declaration of Classes
[AccessSpecifier] Class Identifier
[Inherits BaseClass]
[MemberVariableDeclarations]
End Class

or Private

 BaseClass specifies class that gives the inheritance
 Members could be Dim, Public, Protected , Friend,
or Private

25

Modules
 Like classes, encapsulate data members and
member functions defined within
 Unlike classes, modules can never be instantiated
and do not support inheritance
 Public members declared in a module are
accessible from anywhere in the project without
using their fully qualified names or an Imports
statement
 Known as global members

 Global variables and constants declared in a
module exist throughout the life of the program

26

Declaration of Modules
[AccessSpecifier] Module Identifier
[MemberVariableDeclarations]
End Module

 AccessSpecifier could only be Public or Friend

 Members could be Dim, Public, Protected , Friend,
or Private

27

Scope
 Scope of a declared element is the region in which
it is available and can be referred without using
its fully qualified name or an Imports statement
 Element could be a variable, constant, procedure,
class, structure or an enumeration
 Use care when declaring elements with the same
identifier but with a different scope, because
doing so can lead to unexpected results
 If possible, narrowing the scope of elements when
declaring them is a good programming practice

28

Block Level Scope
 A block is a set of statements terminated by an
End, Else, Loop, or Next statement
 An element declared within a block is accessible
only within that block
 Element could be a variable or a constant
 Even though scope of a block element is limited to
the block, it will exists throughout the procedure
that the block declared

29

Procedure Level Scope
 Also referred to as method level scope
 An element declared within a procedure is
accessible and available only within that
procedure
 Element could be a variable or a constant
 Known as local elements

 All local variables should only be declared using
Dim as the access specifier and are Private by
default

30

Module Level Scope
 Applies equally to modules, classes, and structures
 Scope of an element declared within a module is
determined by the access specifier used at the
declaration
 Elements at this level should be declared outside
of any procedure or block in the module
 Element could be a variable, constant, procedure,
class, structure or an enumeration
 Except for structures, variables declared using
Dim as the access specifier are Private by default

31

Accessibility of Elements
 Accessibility of elements declared at module level

 Public elements
Accessible from
anywhere within the same project and from other
projects that reference the project
 Friend elements
Accessible from within the same project, but not
from outside the project
 Protected elements
Accessible only from within the same class, or from a
class derived from that class
 Private elements
Accessible only from within the same module, class, or
structure

32

Procedures functions structures in VB.Net

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