variables, constants, methods, and calculations chapter 3 - review
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Variables, Constants, Methods, and Calculations
Chapter 3 - Review
Variables
Creating a space in memory to hold data to be utilized while the application is running.
Every variable has a:NameData typeScopeLifetime
Selecting a Data Type for a Variable
Each variable must be assigned a data type
Data type: the type of data the variable can store
Each data type is a class
Selecting a Name for a Variable
Identifier: descriptive name given to a variable
Use a meaningful name that reflects the purpose of the variable
Use Hungarian Notation (intNumber, strName)
Variable names must conform to naming rules (no spaces, no reserved words, start with characters, no punctuation except the underscore _)
Declaring a Variable
Declaration statement: used to declare, or create, a variable
Declaration statement includesScope keyword: Dim or Private or StaticName of the variableData type Initial value (optional)
Assigning Data to an Existing Variable
Assignment statement:Used to assign values to properties of
controlsUsed to assign values to variables
Assignment operator: (=)Value on the right of the = operator is
assigned to the variable on the left of the = operator
Option Explicit ON
Option Explicit ON = must declare (create) the variable before using
Protects against misspelled variable names in code
Placed in the General Declarations section of code editor
Option Explicit ON
Data Typing
Implicit type conversion: can occur if the value on the right side of an assignment statement is not the same data type as the variable on the left side
Example:
25.65 converted to Integer = 26
25.45 converted to Integer = 25
Data Typing
Promoting: when a value is converted to another data type that stores larger numbers
Demoting: when a value is converted to another data type that stores only smaller numbersData loss can occur with demoting
Option Strict ON
Option Strict ON = prevents possible loss of data by not allowing any implicit type conversionsCan be used to enforce correct data typing
Placed in the General Declarations section of the code editor
General Declaration
Program Design
TOE ChartsPseudocodeFlowcharts
All are visual tools to help design the logical flow of the program.
TOE Charts
Task
Object
Event
TOE Charts
TOE Charts help the programmer to think through what the application will do and what it will need to run properly.
1. Input
2. Calculate
3. Print out to screen or paper
4. Clear used data from controls
5. Exit program
TOE Chart – Task
1 – Input
2 – Calculate
3 – Print to screen or paper
4 – Exit program
5 – Clear form
TOE Charts
TOE Charts provide a visual tool to identify the tasks of the application, the objects used in the user interface and the events (clicking, double-clicking) that
trigger the code.TOE Charts identifies the tasks, objects
and events of the FORM.
Perry Primary SchoolMainForm Task Object Event
1.Calculate the sum of and the difference between the two numbers 2.Display the sum and difference in the sumLabel and differenceLabel controls
computeButton Click
End the application exitButton Click
Display the sum and difference (from computeButton)
sumLabel, differenceLabel
None
Get and display two numbers firstTextBox, secondTextBox
None
Display the DialogForm optionsButton Click
Display the SplashScreenForm MainForm LoadDialogForm Task Object Event
Change the color of the MainForm’s text to red
redButton Click
Change the color of the MainForm’s text to black
blackButton Click
SplashScreenForm Task Object Event
Close the SplashScreenForm splashTimer Tick
Pseudocode
Pseudocode identifies the steps of a procedure and writes it in short phases.
Each procedure will have it’s own pseudocode.
Skate-Away Pseudocode
Flowcharts
Flowcharts identifies the steps of a procedure and diagrams it using special symbols.
Flowcharts
Oval – start / stop symbol
Rectangles – process symbols• represents tasks such as making calculations
Parallelogram – input / output symbol• represent input tasks – getting information from user • represent output tasks – displaying information
Lines – flowlines symbol• represents logical flow• connects the symbols
Flowcharts
Flowcharts identifies the steps of a procedure and diagrams it using special symbols.
Each procedure will have it’s own flowchart.
General Design Guide
1. Input
2. Calculate
3. Output (print to screen and/or paper)
4. Clear old data
5. End program
Code Flow
Step – by – step
General Design Guide
1. Input
2. Calculate
3. Output (print to screen and/or paper)
4. Clear old data
5. End program
General Design Guide
1. Input Validate
2. Calculate
3. Output (print to screen and/or paper)
4. Clear old data
5. End program
General Design Guide
1. Input Validate Convert
2. Calculate
3. Output (print to screen and/or paper)
4. Clear old data
5. End program
Using the TryParse MethodMethod: a specific portion of a class’s
instructions that performs a task for the class
TryParse method: Part of every numeric data type’s classUsed to convert a string to that numeric data
type
Using the TryParse MethodTryParse method has 4 arguments
String: string value to be convertedVariable: location to store the result IFormatProvider (optional): specifies
formattingNumberStyles (optional): allows formatting
characters to be in the data to be converted
Using the TryParse MethodMethod: a specific portion of a class’s
instructions that performs a task for the class
TryParse method: Part of every numeric data type’s classUsed to convert a string to that numeric data
type
Using the TryParse MethodTryParse method has 4 arguments
String: string value to be convertedVariable: location to store the result IFormatProvider (optional): specifies
formattingNumberStyles (optional): allows formatting
characters to be in the data to be converted
General Design Guide
1. Input Validate Convert
2. Calculate
3. Output (print to screen and/or paper)
4. Clear old data
5. End program
General Design Guide
1. Input
2. Calculate
3. Output (print to screen and/or paper)
4. Clear old data
5. End program
General Design Guide
Calculate RULE 1: There is an order in which the
computer performs the operation in an expression
RULE 2: All variables must be of the same data type to be able to do mathematical calculations
Arithmetic Operators – Precedence Order
General Design Guide
Calculate RULE 1: There is an order in which the
computer performs the operation in an expression
RULE 2: All variables must be of the same data type to be able to do mathematical calculations
General Design Guide
Calculate RULE 1: There is an order in which the
computer performs the operation in an expression
RULE 2: All variables must be of the same data type to be able to do mathematical calculations
When possible, have the TryParse Method convert the user input (String Data Type) to the numeric data type needed for the calculation.
General Design Guide
1. Input
2. Calculate
3. Output (print to screen and/or paper)
4. Clear old data
5. End program
General Design Guide
1. Input
2. Calculate
3. Output (print to screen and/or paper)
4. Clear old data
5. End program
General Design Guide
1. Input
2. Calculate
3. Output (print to screen and/or paper) Convert data type to STRING Format output
4. Clear old data
5. End program
General Design Guide
Output / Display RULE: Output to be displayed on the
screen must be of the data type STRING.
General Design Guide
Output / Display RULE: Output to be displayed on the
screen must be of the data type STRING. RULE: Values (data) assigned to the Text
Property must be of the data type STRING.
General Design Guide
Output / Display RULE: Output to be displayed on the
screen must be of the data type STRING. RULE: Values (data) assigned to the Text
Property must be of the data type STRING.
Provide proper formatting of the output as required.
Formatting Numeric Output
Formatting: specifying the number of decimal places and any special characters to display
Format specifier: specifies the type of formatting to use (“C”) (“N”) (“D”) (“P”)
Precision specifier: controls the number of significant digits or zeros to the right of the decimal point (“C2”)(“N1”)
Format Specifier
Format Specifier and Precision Specifier
Formatting Numeric Output (continued)
Formatting Numeric Output (continued)
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