CIS-160Final Review

100 points Open book, open notes True/false, multiple choice, fill-in, short

answer

Final Exam

Variable: Memory locations that hold data that can be changed during project execution Example: customer’s name

Named Constant: Memory locations that hold data that cannot be changed during project execution Example: sales tax rate

Variables and Constants

In Visual Basic when you declare a Variable or Named Constant An area of memory is reserved A name is assigned called an Identifier

Using Variables and Constants

Assign name and data type Not executable statements unless a value is

assigned on same line

Declaration Statements

Must follow Visual Basic Naming Rules Cannot use reserved words or keywords that Basic

has assigned a meaning such as print, name, and value

Must begin with a letter and no spaces or periods Should follow Naming Conventions

Names should be meaningful Include class (data type) of variable in name

Use mixed case for variables and uppercase for constants

Naming Variables & Constants

Visibility of a variable is its scope Where is that identifier valid?

Scope may be Namespace: throughout project Module: within current form/class Local: within a procedure Block: within a portion of a procedure

Lifetime of a variable is the period of time the variable exists

Scope and Lifetime of Variables

Use static to declare local and block level variables that need to retain their value

Variable will not be initialized next time procedure runs, and will have last value assigned

If the variable is used in multiple procedures, declare it at the module level with private Pass data as arguments if one procedure calls

the other

Static Variables

Use Parse methods to convert a string to its numeric value before it’s used in a calculation

Each numeric data type class has a Parse method

Parse method returns a value that can be used in calculations

Parse method fails if user enters nonnumeric data, leaves data blank, or entry exceeds data type size

Converting Strings to Numeric Values

Enclose statements that might cause a run-time error within Try/Catch block

If an exception occurs while statements in the Try block are executing, code execution is moved to the Catch Block

If a Finally statement is included, the code in that section executes last, whether or not an exception occurred

Try/Catch Blocks

This OOP feature allows the Messagebox Show method to act differently for different arguments

Each argument list is called a signature: the Show method has multiple signatures

Supplied arguments must exactly match one of the signatures provided by the method

Using Overloaded Methods

Used to make decisions If true, only the Then clause is executed; if

false, only Else clause is executed (if there is an Else)

Block If…Then…Else must always conclude with End If

Then must be on same line as If or ElseIf End If and Else appear alone on a line

If Statements

Test in an If statement is typically based on a condition

Six relational operators are used for comparison of numbers, dates, and text Equal sign is used to test for equality

Strings are compared using ANSI value of each character CIS is less than CNA MATH is less than MATH&

Conditions

Compound conditions can combine multiple logical conditions And describes conditions where both tests are

true Or describes conditions where either or both tests

are true When both And and Or are evaluated And is

evaluated before the Or Use parenthesis to change the order of evaluation

Combining Logical Operators

Check to see if valid values were entered or available

Can check for a range of values (often called “reasonableness”)If Integer.Parse(scoreTextBox.Text) >= 0 Then

‘ Code to perform calculations…. Check for a required field (not blank)

If studentIDTextBox.Text <> "" Then ...

Input Validation

Use Select Case to test one value for different matches (“cases”)

Usually simpler and clearer than nested If No limit to number of statements that follow a

Case statement When using a relational operator must use the

word Is Use the word “To” to indicate a range with two

endpoints

Select Case

Add object/event combinations to the Handles clause at the top of an event procedure

Allows the procedure to be associated with different events or other controls

Sender argument identifies which object had the event happen

Cast (convert) sender to a specific object type using the CType function

Sharing an Event Procedure

Calling an event procedure allows reuse of code

[Call] ProcedureName (arguments) Keyword Call is optional and rarely used

ExamplesCall clearButton_Click (sender, e)--OR--clearButton_Click (sender, e)

Calling Event Procedures

Breakpoints allow you to follow the execution of your code while program is running Can hover the cursor over a variable or property to

see the current value in the current procedure Can execute each line, skip procedures

Can use Console.Writeline to output values to track code execution

Variables and property values can be seen in different windows (autos, locals) while code is executing

Breakpoints

A general procedure is reusable code which can be called from multiple procedures

Useful for breaking down large sections of code into smaller units

Two types: Sub Procedure performs actions Function Procedure performs actions AND

returns a value (the return value)

Writing Procedures

If a procedure includes an argument, any call to the procedure must supply a value for the argument Number of arguments, sequence and data type must

match Arguments are passed one of two ways:

ByVal – Sends a copy of the argument’s value, original cannot be altered

ByRef - Sends a reference to the memory location where the original is stored and the procedure may change the argument’s original value

If not specified, arguments are passed by value

Passing Arguments to Procedures

Show method displays a form as modeless - means that both forms are open and the user can move from one form to the other

ShowDialog method displays a new form as modal - the user must close the form in order to return to the original form No other program code in the original form can

execute until the user responds to and hides or closes the modal form

Modal versus Modeless Forms

Provide the user with a list of choices to select from

Various styles of display, choose based on Space available Need to select from an existing list Need to add to a list

Listboxes and comboboxes share most of the same properties and operate in a similar way Combo box control has a DropDown Style property Combo box allows text entry

ListBoxes and ComboBoxes

List of items in a ListBox or ComboBox is a collection Collection is group of like objects Items referenced by number (zero-based)

Collections are objects that have properties and methods that allow Adding items Removing items Referring to an individual element/member Counting items

The Items Collection

Index number of currently selected item is stored in the SelectedIndex property Property is zero-based If no list item is selected, SelectedIndex

property is negative 1 (-1) Use to select an item in list or deselect all

items

SelectedIndex

A loop repeats a series of instructions An iteration is a single execution of the

statement(s) in the loop Used when the exact number of iterations is

unknown A Do/Loop terminates based on condition change Execution of the loop continues while a condition is

True or until a condition is True The condition can be placed at the top or the

bottom of the loop

Do Loops

Pretest: test before enter loop loop may never be executed since test

executes BEFORE entering loop Do While … Loop Do Until … Loop

Posttest: test at end of loop loop will always be executed at least once Do … Loop While Do … Loop Until

Pretest vs. Posttest

Used to repeat statements in a loop a specific number of times

Uses a numeric counter variable called Counter or Loop Index Counter is incremented at the bottom of the loop on each

iteration Start value sets initial value for counter End value sets final value for counter Step value can be included to specify the incrementing

amount Step can be a negative number

For/Next Loops

Used to repeat statements for each member of a group

A reference variable is used to “point” to each item

Must be the data type of each item in group

For/Each Loops

In some situations you may need to exit the loop early

Use the Exit For or Exit Do statement inside the loop

Typically used in an If statement (some condition determines whether to exit the loop or not)

Exiting Loops

List or series of variables all referenced by the same name Similar to list of values for list boxes and

combo boxes, without the box Each variable is distinguished by an index Each variable is the same data type

Individual elements are treated the same as any other individual variable

Arrays

Element: Individual item in the array Subscript (or index): Zero-based identifier

used to reference the specific elements in the array Must be an integer

Subscript Boundaries Lower Subscript, 0 by default Upper Subscript

Array Terms

Subscripts may be constants, variables, or numeric expressions

Subscripts must be integers Subscripts begin at zero (0) VB throws exceptions for subscripts that are

out of range (upper and lower bounds).

Subscripts