Chapter 3 Key Terms

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Chapter 3 Key Terms
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argument

• Generally, the values we work with or process.
• The subject of a function or method.
• Example temperatureTextBox.Select(5,2)
• TextBox Method highlights the 2 characters
  starting right after character position
  5(characters 6 and 7).

3
assignment operator

• The equal sign "" is the assignment operator.
• Most often, assignment statements are used to
  fill variables or a property with a value.
• Example
• nameString "Thomas the Tank Engine"

4
block level variable

• Declared inside a block of code
• Declared every time the block of code runs.
• Recognized only within the block in which it is
  declared.
• Has the smallest scope of all variables.

5
Casting

• An explicit (deliberate) converstion.
• Example
• ageTextBox.Text Convert.ToString(ageInteger)
• converts the integer value of ageInteger to a
  string which fills the ageTextBox.Text property.
• Should be tested to be sure no significant digits
  are lost.

6
Named Constant

• Memory locations of numbers that cannot change at
  run time.
• Use all caps for a named constant.
• Use underscore to separate words.
• PRICE_PER_KWH_Decimal .12D
• Assignment requires the type declaration
  character (D,R,I,L,S,F)

7
exception

• A run time error.
• Statements that might cause an exception should
  be place in the Try / Catch block.

8
format

• The predetermined way an output number will look
  to the user.
• Controlled by the format specifier code.
• Example currency formatted string from a decimal
  type.
• someTextBox.Text someDecimal.ToString("C")
• causes the value of someDecimal to be displayed
  with , commas, and two decimal places.
• See VB Help "format specifier numeric" for more
  ToString argument codes.

9
identifier

• The name you give to variables and constants.
• The declared name of any object.

10
implicit converstion

• No special syntax is used.
• Allows a widening conversion
• Example
• someTextBox.Text numeratorDecimal
• See VB Help "widening converstions"
• A narrowing converstion is risky and not allowed
  when Option Strict is On.

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Intrinsic Constant

• System defined constants.
• See Color class
• See MessageBox class
• See Math class for pi and e

12
lifetime of a variable

• The time between events that a variable remains
  declared.
• A local (block) variable (declared within the
  block) remains declared only during the execution
  of the block.
• A module-level (form-level) usually remains
  declared as long as the application is running.

13
Message Box

• For displaying messages (duh).
• It has but one method Show
• Bare bones Example
• MessageBox.Show("Are you sure?")
• MessageBox is modal. User can do nothing else
  until a button in the box is clicked. That kind
  of demands attention.

14
namespace level variable

• project wide scope and lifetime
• programmers prefer to minimize the limits scope
  and lifetime
• namespace variable will be rare in the programs
  we write in this course.

15
Try and Catch blocks

• The Try block contains statements susceptible to
  run-time errors (exceptions).
• The Catch block contains statements for recovery
  from run-time errors (maybe a scolding
  MessageBox, maybe clearing offensive input, maybe
  returning focus).
• After a Catch, program control automatically
  returns to the Try block.

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Option Explicit Off

• Programmer must declare all variables before
  using them.
• It is unwise to remove Option Explicit because
  you could inadvertently declare a new variable by
  misspelling an existing variable.

17
Option Strict On

• Prohibits downsize implicit conversions
• Unwise to allow implicit conversions.
• Option Strict On should be your first line of
  code.
• To make Strict and Explicit automatic
• VB2003 Click ProjectgtPropertiesgtCompile
• VB2005 Click ToolsgtOptions

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math order of operations

• inside the innermost parentheses
• exponentiation
• multiply and divide
• integer division
• modulus
• add and subtract
• work is done from left to right

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overloading

• the capacity to use arguments of various
  signatures (number and types of arguments).
• See MessageBox in Chapter 3 for example.

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strongly typed

• Option Strict is ON.