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