Introduction to vb programming
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Introduction to VB Programming. Chapter 3. Quotes for Today. When faced with a decision, I always ask, “What would be the most fun?” Peggy Walker It is a capital mistake to theorize before one has data. Arthur Conan Doyle. Creating a Project With Code. A Simple Program.

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Introduction to vb programming

Introduction to VB Programming

Chapter 3

VBN2008-03


Quotes for today

Quotes for Today

When faced with a decision, I always ask, “What would be the most fun?”

Peggy Walker

It is a capital mistake to theorize before one has data.

Arthur Conan Doyle

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Creating a project with code

Creating a Project With Code

A Simple Program

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Two types of applications 2 of the many

Two Types of Applications(2 of the many)

  • Windows Applications

    • Access Windows environment

  • Console Applications

    • Access DOS environment

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Anatomy of a simple program

‘ Welcome1.vb

‘ Simple Visual Basic program

Module modFirstWelcome

Sub Main()‘entry point of program

‘() indicates a procedure

Console.WriteLine(“Welcome to Visual Basic!”)

End Sub ‘Ends Main Procedure

End Module‘Ends modFirstWelcome

Anatomy of a Simple Program

Green=

Comments

Identifiers

Keywords

Class Method String

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A module

A Module

  • Collectively called a module definition

  • Console modules consist of logical groupings of procedures

    • simplify program organization

  • Convention:

    • Begin all modules with “mod”

      • Example:modWelcome

    • Not case sensitive

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An identifier

An Identifier

  • A series of characters

    • Consist of letters, digits & underscores (_)

    • Not case sensitive

  • Cannot

    • Begin with a digit

    • Contain spaces

  • Examples

    • Valid: modFirstWelcome, num1, SalesTax

    • Invalid: 123xyz, My Tax, 753 Room

Primitive Data Types:

BooleanByteChar

DateDecimalDouble

IntegerLongSbyte

ShortSingleString

UintegerUlongUShort

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A keyword reserved word

A Keyword (Reserved Word)

  • A particular word that has a specific meaning within each programming language

  • Examples:

    • Module, End, Sub, If, For, Loop

    • For more examples refer to Pages 76

    • Not case sensitive, but VB will automatically convert to “proper” case

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Keywords or reserved words

Keywords (or Reserved Words)

  • Do not try to use these words as variable names.

    • Misspelling a keyword may cause a syntax error

    • VB will assume you are creating a new identifier.

    • But…the program will not work correctly.

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Spacing whitespace

Spacing (Whitespace)

  • VB ignores spaces and tabs between identifiers

    • Vertically and horizontally

  • Use vertical blank lines, tabs and horizontal spaces to make projects easier to read.

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Statements

Statements

  • Console.WriteLine(“Hi!”)

    • (“Hi”) is the argument

      • Note the dot notation…

    • Classes organize groups of related methods

      • WriteLine is the method

      • Console is the class to which the method belongs

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The simple program revised

The Simple Program Revised

  • Pg 78;

    • File>New Project>Console Application

    • Name = WelcomeConsole

    • Program Name = Welcome1.vb

    • Reserved words are blue, text is black

    • Change name of Module to ModWelcome

    • Writing code

    • Run program

  • Tools>Options personalizes environment

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Features

Features

  • IntelliSense

    • When the dot (.) is keyed after Console, a list of available methods is displayed

    • Options

      • List Members – lists the members of an object.

      • Parameter Info – Lists the members of an object.

      • Quick Info – displays information in tool tips as the mouse rests on elements in your code.

      • Complete Word – completes typed words

      • Automatic Brace Matching – adds parentheses or braces as needed.

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Documenting code

Documenting Code

Commenting…

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Consistency consistency

Consistency, Consistency!

  • Just as important as commenting code

  • Reduces reader frustration

  • Makes comments & code

    • easier to understand

  • Makes debugging

    • easier

    • faster

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Commenting code

Commenting Code

  • Used to identify the purpose of a piece of code, the author, creation date, requirements

    • Required in this class!

  • Indicator is the apostrophe.

    • Ex.‘This is a comment.

  • The default color for VB is green.

    • Note: for those of you who might be colorblind to green, the comment color property can be changed within the environment controls. But…Don’t do it in here or in the Lab…

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Comments

Comments

  • Explains

    • what is going on or

    • what is being described

  • Denoted by a single quotation mark (‘)

  • Example

    ‘Input variable

    Dim Principal As Single‘The original loan amount

    Dim Address As String‘Shipping address for client

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Comment levels

Comment Levels

  • Application Level

    • Name - name of application

    • Author/Company - who created it

    • Add-ins - are there any other modules or code objects necessary to run this program

    • Purpose of Program - what is the program supposed to do?

    • System Requirements - what is the system upon which this program will operate

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Comment levels1

Comment Levels

  • Module Level

    • Necessary when multiple programmers are working on a project.

    • Useful when planning to reuse the code.

    • Same parameters as before, but with addition of

      • Dependencies –

        • declares what is required as input for the module to work (Passing parameters)

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Comment levels2

Comment Levels

  • Procedure Level

    • Used to describe to programmers what the procedure does and how it does it.

    • Used for user-defined and non-obvious procedures and functions.

      • Ex. A new form of the Square Root function

    • Helps during a multi-programmer project

      • Lets other programmers know who to contact when there are questions or problems with the code.

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Comment levels3

Comment Levels

  • Code Level

    • To specify what a piece code is doing

    • To specify that a piece of code needs further attention

    • Use these as suggestions for consistency

      • ‘Generic comment - explanation

      • ‘???Questionable code - useful for debugging

      • ‘!!!Code requires attention - useful for reminders or where to provide additional work.

      • ‘-MLM-Include your initials for comment referencing

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Comment comment comment

Comment, Comment, Comment!

  • Provides

    • meaning to code

    • additional information to other programmers

    • reasons why one method was used over another for future maintenance

  • Makes Maintenance EASIER!

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Console writeline revisited

Console.WriteLine Revisited

  • Dim number1 as Integer

  • Number1 = Console.ReadLine()

    • ReadLine() is a method that causes the program to pause and wait for user input.

    • After the value is entered by keyboard, the user presses the Enter key to send the value to the program.

  • Example:

    Console.WriteLine(“The sum is ” & sumofNumbers)

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Basic components of vb

Basic Components of VB

Variables &Assignment Statements

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Variables

Variables

  • A Variable

    • Is a temporary storage location for information

    • Clears upon exit of either the program or the procedure

    • Examples:

      • SumSalesTaxSquareRoot

      • CountSales_TaxPrincipal

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Variable declarations

Variable Declarations

  • Name of a variable is any valid identifier

    • Cannot be keywords

    • Maximum length is 255 characters

    • Must begin with a letter

    • Must contain only letters, numbers and underscores.

    • VB is not case sensitive so

      • uppercase and lowercase letters are treated in the same way.

  • Variable’s Type - what type of information each variable may contain.

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Variable declarations1

Variable Declarations

  • Declaration of Variables

    • Provides the Variable Name and its data type

    • Ex.DimsumAsInteger

    • VB always initializes variables to Zero for numbers and the Null set for characters and strings

Variable Identifier

Variable’s Data Type

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Variable data types

Variable Data Types

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Variable declarations changes from vb6 to vb net

Variable Declarations Changes from VB6 to VB.Net

  • New data types

    • Char

    • Unsigned Integers

      • Ulong - 8 bytes

      • Uinteger - 4 bytes

      • Ushort - 2 bytes

      • Sbyte - 1 byte

  • Lost data types

    • Currency

    • Variant – A great thing!

    • Image (use PictureBox instead)

  • Note about Unsigned Integers - They are non-CLS compliant and not supported by all .Net languages

    • --Avoid using--

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More changes from vb6 to vb net

More Changes from VB6 to VB.Net

  • Replacements

    • RadioButtons replaces OptionButton

    • GroupBox replaces Frame

    • SelectedIndex in ListBox replaces ListIndex

    • Images are added to PictureBox’s by using the System.Drawing.Image.FromFile method

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Variable declarations2

Variable Declarations

  • Declarations made

    • in the General DeclarationSection are available throughout the entire program.

      • This is Global Scope.

    • inside a procedure are available only within the procedure

      • This is Local Scope.

  • Both will be discussed in more detail later.

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Assignment statements

Assignment Statements

  • Assigns a value, variable or expression to a variable

    • Syntax: VariableName = value or variable or expression

    • A variable is placed on the left of the equal sign (=)

      • Think of the “=” as “takes on the value of”

    • The value to be stored in the variable appears on the right.

      • The value is made up of the following:

        • A value

        • An expression

        • A variable (Identifier)

    • Ex.sum = count + 3

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Assignment statements1

Assignment Statements

  • When a value is stored in a variable (on the left side of the assignment operator), it replaces the existing data.

    • This is known as destructive read-in.

      • Ex.sum= 3 + 5

  • When a variable is used (on the right side of the assignment operator), the value stored in the variable is preserved.

    • This is known as nondestructive read-in.

      • Ex.sum = count + 1

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Arithmetic in vb

Arithmetic in VB

And Operator Precedence

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Arithmetic in vb1

Arithmetic in VB

  • The arithmetic operators used in VB use several special characters:

    • ^ indicates exponentiation

    • * indicates multiplication

    • \ indicates Integer division

  • Arithmetic expressions are written in straight-line form.

    • Ex.a ^ b

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Arithmetic in vb2

Arithmetic in VB

  • Most operators are binary, requiring 2 operands.

    • Ex.sum + value

  • However, the unary operator (+, -) requires only one operand.

    • Ex.-3, +3

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Arithmetic operators

Arithmetic Operators

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Special arithmetic operators

Special Arithmetic Operators

  • Integer Division (\)

    • Supports Byte, Short, Integer, or Long Data Types

    • results in an Integer result

      • Ex.8 \ 2 = 4 and 9 \5 = 1

    • Note: Floating point numbers are coerced to Long (a narrowing conversion) quietly (behind the scene) before Integer Division takes place.

      • Ex.7.7\4 = 2 because 8 \ 4 = 2.

      • the whole part of the floating point result and the rest is truncated.

Weird!

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Integer division examples

Integer Division Examples

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Special arithmetic operators1

Special Arithmetic Operators

  • Modulus (Mod) results in an Integer remainder after Integer Division.

    • Ex.X Mod Y = the remainder after X is divided by Y. If the result is 0, then X is evenly divisible by Y.

    • Ex.10 Mod 4 = 2; 10.8 Mod 4 = 3

  • Note:

    • if the Result is defined as a floating point, the result will be the floating point remainder

    • Use of the Mod with floating point will introduce a hidden conversion from Single or Double to Integer – possible loss of data

Weird!

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Modulus examples

2

4 ) 10

8

2

2

4.8) 10.0

10

0

4.8 rounds to 5

Modulus Examples

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Modulus examples1

2

5 ) 12.6

10

2.6

Modulus Examples

5

9.35) 47.90

46.75

1.15

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Comparison operators

Comparison Operators

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Operator precedence

Operator Precedence

  • Reflects a hierarchical order

  • Aids evaluation of expressions

    • Boolean Relational Operators have the lowest precedence. (to be discussed later)

  • Using parentheses ( )is recommended to:

    • Avoid syntax errors

    • Clarify the meaning of the comparison

  • Evaluation Trees are used to check logic

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Order of operator precedence

Order of Operator Precedence

See Appendix A

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Line continuation

Line Continuation

  • Permits a long line of code to be divided into two lines.

    • Must be surrounded by at least one space

    • Must not have anything after the “_”

  • Improves readability

  • Example:

    MessageBox.Show(“The Square Root of 2 is “ & root, _ “The Square Root of 2”)

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String concatenation

String Concatenation

  • Concatenation Operator is the ampersand “&”

  • Is a binary operator

  • Combines two strings

  • Example:

    MessageBox.Show(“The square root of 2 is ” & root)

    • Note: If the variable (in this case root) is not a String, VB will automatically create a String representation of the argument.

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Common programming errors

Common Programming Errors

Syntax Errors

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Syntax errors

Syntax Errors

  • A syntax error, also called a compile error, is a violation of a language’s syntax.

  • Occurs when:

    • statements are missing information

    • statements have extra information

    • names are misspelled

    • punctuation is missing (missing parentheses)

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Syntax errors help

Syntax Errors - Help

  • VB

    • indicates syntax errors by underlining the suspect code with a red line

    • provides an explanation in the Task List window

    • Provides a tool tip explaining what VB.Net thinks is wrong, if you rest the mouse on the error.

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Introduction to vb programming

Next?

Classes &

Objects

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