Visual Programming with Visual Programming with Visual Basic .NETVisual Basic .NET

Visual Programming with Visual Programming with Visual Basic .NETVisual Basic .NET

Procedures, Functions and StructuresProcedures, Functions and Structures

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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

Example

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

here3

Boss

Worker2

Worker4

Worker5

Worker3

Worker1

Click Here for more details

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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

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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

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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

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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

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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

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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

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Declaration of Function Procedures

Declaration syntax [AccessSpecifier] Function _ Identifier([ParameterList]) [As DataType]

[Statements]Return ReturnExpression End Function

AccessSpecifier could be Public, Protected, Friend, 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

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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

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Declaration of Structures

Declaration syntax [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.

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Variables of Composite Data Types

Variables of composite data types can be declared with the data types defined as the structures

Declaration syntax 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

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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])

Methods of Math Class

Function procedures (Methods) contained in class “Math”

Performs mathematical operations and returns a value

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Method Description Example

Abs(x) Returns the absolute value of xAbs(-23.5) is 23.5

Ceiling(x)Rounds x to the smallest integer not less than x

Ceiling(9.2) is 10.0

Cos(x)Returns trigonometric cosine of x

Cos(0.0) is 1.0

Exp(x) Returns the exponential ex

Exp(1.0) is 2.72828182845905 approximately

Methods of Math Class

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Method Description Example

Floor(x)Rounds x to the largest integer not greater than x

Floor(9.2) is 9.0

Log(x)Returns the natural logarithm of x (base e)

Log(2.71828182845905) is 1.0 app.

Max(x,y)Returns the maximum value of x & y

Max (5,8) is 8

Min(x,y)Returns the minimum value of x & y

Min(5,8) is 5

Pow(x,y) Calculates x raised to power yPow(2.0,7.0) is 128

Sin(x)Returns the trigonometric sine of x

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

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

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Methods of String Class

Two types Shared Methods – No Need to mention the instance name

If Compare(strA,strB) > 0 Then …

Non shared Methods - Needs to mention the instance name

If myString.EndsWith(“ed”) Then …

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Method DescriptionEndsWith(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

Functions to Determine Data Type

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Method DescriptionIsArray(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 NothingChecks whether the object is set to nothingIf objMyObject Is Nothing Then …

TypeOfChecks the type of an object variableIf TypeOf txtName is TextBox Then …

TypeName(Variable Name)

Returns the data type of a non object type variable

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

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Date / Time Functions

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Method DescriptionDate 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

In Built String Functions

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Function Description Example InStr Finds the starting position of a substring

within a string InStr(“My mother”, “mo”) = 4

LCase Converts a string to lower case LCase(“UPPER Case”) = upper case Left Finds or removes a specified number of

characters from the beginning of a string Left(“Kelaniya”, 6) = “Kelani”

Len Gives the length of a string Len(“Hello”) = 5 LTrim Removes spaces from the beginning of a

string LTrim(“ Hello “) = “Hello “

Mid Finds or removes characters from a string

Mid(“microsoft”,3,4) = “cros”

StrReverse Reverses the strings strReverse(“Kelaniya”) = “ayinaleK” Right Finds or removes a specified number of

characters from the end of a string Right(“Kelaniya”, 6) = “laniya”

RTrim Removes spaces from the end of a string RTrim(“ Hello “) = “ Hello“ Str Returns the string equivalent of a

number Str(12345) = “12345”

Trim Trims spaces from both the beginning and end of a string

Trim(“ Hello “) = “Hello“

UCase Converts a string to upper case UCase(“lower Case”) = “UPPER CASE”

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

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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

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Declaration of Classes

Declaration syntax [AccessSpecifier] Class Identifier

[Inherits BaseClass] [MemberVariableDeclarations]

[MemberFunctionDeclarations] End Class

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

BaseClass specifies class that gives the inheritance

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

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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

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Declaration of Modules

Declaration syntax [AccessSpecifier] Module Identifier

[MemberVariableDeclarations][MemberFunctionDeclarations] End Module

AccessSpecifier could only be Public or Friend If omitted, it is Friend by default

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

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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

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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

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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

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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

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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