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Objectives Declare both a variable and a named constant
Write an assignment statement Use the Convert class methods to convert data to an appropriate type Write arithmetic expressions Understand the scope of both a variable and a named constant Microsoft Visual Basic .NET: Reloaded

Objectives (continued)
Include internal documentation in the code Use the Option Strict and Option Explicit statements Use a TOE chart to code an application Use pseudocode and a flowchart to plan an object’s code Send focus to a control Microsoft Visual Basic .NET: Reloaded

Objectives (continued)
Explain the difference between syntax errors and logic errors Format an application’s numeric output Microsoft Visual Basic .NET: Reloaded

Variables Computer memory locations where users can temporarily store data Must be assigned a data type by programmer Data type determines type of data variable can store Contents can change as application runs Microsoft Visual Basic .NET: Reloaded

Selecting a Data Type for a Variable
Microsoft Visual Basic .NET: Reloaded

Selecting a Data Type for a Variable (continued)
Integers  whole numbers Integer, Long, Short Floating-point numbers  real numbers Single, Double – use exponential notation Example: = 3.2E4 Decimal  uses fixed decimal point Character Types Char – one character String – 0 to 2 billion characters Microsoft Visual Basic .NET: Reloaded

Selecting a Name for a Variable
Name should be descriptive Use three-letter prefix Use “m” for “module-scope” variables Punctuate using Pascal-case Type m and 3 letter prefix using lowercase, then capitalize the first letter of each word in the variable name Microsoft Visual Basic .NET: Reloaded

Selecting a Name for a Variable (continued)

Declaring a Variable Microsoft Visual Basic .NET: Reloaded

Declaring a Variable (continued)
accessibility variablename as [datatype = initialvalue] accessibility - sets scope of variable Dim, Public, Private variablename = programmer chosen name datatype = data type of the variable Anything in brackets is optional initialvalue = default value at start of program If no value specified numeric types = 0, character types = Nothing, boolean = false Microsoft Visual Basic .NET: Reloaded

Assigning Data to an Existing Variable
assignment statement strName = “Mary” intAge = 35 “=“ sign is called assignment operator Literal constant – value does not change Number 35 is numeric literal constant “Mary” is a string literal constant String - a group of characters enclosed in quotes Microsoft Visual Basic .NET: Reloaded

Assigning Data to an Existing Variable (continued)

Assigning Data to an Existing Variable (continued)
Literal type characters force literal constants to assume new data type Microsoft Visual Basic .NET: Reloaded

Using the Convert Class
Convert class creates object that is either a number or a string by converting value to a specified data type and returning result strAge = Convert.ToString(intAge) Microsoft Visual Basic .NET: Reloaded

Writing Arithmetic Expressions
Precedence number indicates order in which VB performs operation in an expression Microsoft Visual Basic .NET: Reloaded

Writing Arithmetic Expressions (continued)
Integer division operator (\) Returns integer portion of division discarding remainder 8\3 results in answer of 2 Modulus arithmetic operator (Mod) Returns remainder portion of division discarding integer portion 7 Mod 3 results in an answer of 1 Often used to determine Leap years Valid only with division of integer values Microsoft Visual Basic .NET: Reloaded

How To… Microsoft Visual Basic .NET: Reloaded

The Scope and Lifetime of a Variable
Indicates where in the application’s code the variable can be used Lifetime Indicates how long the variable remains in the computer’s internal memory Microsoft Visual Basic .NET: Reloaded

The Scope and Lifetime of a Variable (continued)
Procedure Scope Procedure-level variable Variable declared within a procedure Variable can only be used in procedure in which declared Module scope Module-level variable Variable declared in General Declarations section of the form Variable can be used within all procedures in the form Microsoft Visual Basic .NET: Reloaded

Procedure-level variables example

Module-level variable example

The Scope and Lifetime of a Variable (continued)
Block scope Block-level variable Declared inside specific blocks of code If…Then…Else or For….Next Can be used only inside the block in which declared Microsoft Visual Basic .NET: Reloaded

Named Constants A memory location inside a computer whose value cannot be changed while the application is running Microsoft Visual Basic .NET: Reloaded

Named Constants (continued)

Internally Documenting the Program Code
Internal documentation: Term used by programmers for comments placed in code Place an apostrophe (‘) before text you want treated as internal documentation (comment) VB ignores everything after apostrophe on line Place comments at beginning of each procedure Microsoft Visual Basic .NET: Reloaded

Internally Documenting the Program Code (continued)
Include comments: as necessary to explain various sections of code at beginning of application explaining application’s: Name Purpose Author Date of creation or modification Microsoft Visual Basic .NET: Reloaded

Internally Documenting the Program Code (continued)

Option Explicit and Option Strict
Option Explicit On Tells computer to warn you if your code contains name of an undeclared variable Prevents unintentional declaration of variables which automatically are of type Object Option Strict On Tells computer not to perform any implicit type conversions which may lead to loss of data Implicit type conversions are automatic conversions from one data type to another performed by the computer to fit data into an assigned memory location Microsoft Visual Basic .NET: Reloaded

Option Explicit and Option Strict (continued)

Coding the SKATE-AWAY SALES Application
Application calculates and displays total number of skateboards ordered and total price of skateboards including 5% sales tax Planning steps: Identify tasks the application needs to perform Identify objects to which you will assign those tasks Identify events required to trigger an object into performing its assigned tasks Design the user interface Microsoft Visual Basic .NET: Reloaded

Coding the SKATE-AWAY SALES Application (continued)

Using Pseudocode to Plan a Procedure
Pseudocode: short phrases to describe steps a procedure needs to take to accomplish its goal Microsoft Visual Basic .NET: Reloaded

Using a Flowchart to Plan a Procedure
Flowchart – uses standardized symbols to show steps procedure must follow to reach its goal Standard symbols utilized: Flowlines - connection lines between symbols Start/stop – ovals indicating starting and ending points of procedure Process – rectangles designating tasks such as calculations Input/Output – parallelogram designating input and output tasks such as getting information from user Microsoft Visual Basic .NET: Reloaded

Using a Flowchart to Plan a Procedure (continued)

Using a Flowchart to Plan a Procedure (continued)
Coding the one task of bntExit_Click event using either pseudocode or flowchart tools Microsoft Visual Basic .NET: Reloaded

Coding the btnClear control’s Click Event Procedure

Assigning a Value to the Property of a Control
Zero-length string “” Also called empty string Set of quotation marks with nothing between them Assigned to the text property of a control at run-time removes contents of control Me.txtname.Text Me refers to the current form txtName refers to a textbox control on the form Text refers to a property of the txtName control Microsoft Visual Basic .NET: Reloaded

HOW TO… Microsoft Visual Basic .NET: Reloaded

Using the Focus Method Focus indicates the control that can accept input and/or is awaiting an action from user Microsoft Visual Basic .NET: Reloaded

btnClear_Click Event Procedure code

Coding the btnCalc Control’s Click Event Procedure

Coding the btnCalc Control’s Click Event Procedure (continued)

Completed Code for Application

Completed Code for Application (continued)

Testing and Debugging the Application
Invalid data - data the application is not expecting Debugging: Process of locating syntax and logic errors in the program Syntax errors Typographical errors that violate rules governing valid syntax of the language Me.Colse() instead of Me.Close() Logic errors Instruction that does not give expected results decAverage = decNum1 + decNum2 / 2 Microsoft Visual Basic .NET: Reloaded

Testing and Debugging the Application (continued)
First test with valid data Microsoft Visual Basic .NET: Reloaded

Testing and Debugging the Application (continued)
Then test with invalid data Microsoft Visual Basic .NET: Reloaded

Formatting Numeric Output
Specifying number of decimal places and special characters to display in a number Format string: String used to specify format Example: “Axx” must be enclosed in quotes Format specifier - A Alphabetic character that specifies format you wish to use Precision specifier – xx xx is the sequence of digits desired Microsoft Visual Basic .NET: Reloaded

Formatting Numeric Output (continued)

Programming Example – Currency Calculator
Application allows user to enter number of American dollars that he or she wants to convert to British pounds and Mexican pesos Make appropriate calculations and then display results on screen Microsoft Visual Basic .NET: Reloaded

TOE Chart Microsoft Visual Basic .NET: Reloaded

User Interface Microsoft Visual Basic .NET: Reloaded

Objects, Properties, and Settings

Tab Order Microsoft Visual Basic .NET: Reloaded

Pseudocode btnExit Click event procedure close application
btnCalc Click event procedure 1. assign input value to a variable 2. calculate number of British pounds by multiplying American dollars by 3. calculate number of Mexican pesos by multiplying American dollars by 4.display number of British pound and Mexican pesos in lblBritish and lblMexican 5.send the focus to the txtAmerican text box Microsoft Visual Basic .NET: Reloaded

Code Microsoft Visual Basic .NET: Reloaded

Code (continued) Microsoft Visual Basic .NET: Reloaded

Summary Variables and named constants are computer memory locations that store data Variables are declared with a name and data type Scope refers to where a program can access a variable or named constant Module scope variables can be accessed anywhere in the module Procedure scope variables can only be accessed in the procedure in which declared Block scope variables can only be accessed within the block in which declared Microsoft Visual Basic .NET: Reloaded

Summary (continued) Lifetime refers to how long a variable remains in the computer’s memory Literal constants are items of data Convert class contains methods to convert values to a specified data type Integer division operator divides 2 integers and returns the result discarding any remainder Modulus division operator divides 2 integers and returns the remainder Microsoft Visual Basic .NET: Reloaded

Summary (continued) Option Explicit warns if undeclared variables are used Option Strict prevents implicit type conversions that may result in loss of data Use pseudocode (short phrases) or flowcharts (standardized symbols) to plan the application Test application with both valid and invalid data Format numeric output to display special characters Microsoft Visual Basic .NET: Reloaded

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