Programming continued

1
Programming (continued)

• Chapters 3.4, 5.1, and 5.2
• http//www.cs.pitt.edu/bmills/cs4/

2
Administration

• Mailing List
• Programming Assignment 1
• Will be posted today/tomorrow
• We will discuss on Wednesday
• First part due Monday
• Quiz Today

3
Brief Review

• Math Operations (,-,/,,mod,math.sqrt)
• Defining Variables
• Dim x as String
• Assigning Variables
• Dim x as String bryan
• String Functions
• Concatenation -
• fan.Length 3
• fan.toUpper FAN
• fanatic.IndexOf(a) 1
• Visual.Substring(3,2) ua

4
Event Procedures

• Private Sub btnOne_Click() Handles btnOne.Click
• First, some terminology
• procedure, subroutine, function, method,
  subprogram
• Portion of larger program designed for a task
  that is relatively independent of the larger
  program
• Some languages make distinctions
• Technically, VB does, but well worry about this
  later
• The Sub above actually stands for Subroutine
• btnOne is the actual object this deals with
• Click is the event it handles for that object

5
Blocks of Code

• Code is divided into blocks of code in Visual
  basic
• Private Sub foo(x)
• If x gt 100 Then
• A Block Here
• End If
• End Sub

6
Types of Errors

• Syntax
• Runtime (trying to do math on strings)
• Logical (integer division)

7
Types of Errors

• Syntax
• These errors are caused when something is
  misspelled, punctuation is missing, etc.
• Dim x as Ineger
• x5 12
• My foo blat fe fi
• x x 5
• jnk_box.Text - Text box is really junk_box

8
Types of Errors

• Runtime
• Not picked up by VB until execution of the
  program
• User entered strings and you tried to multiple
  them
• User enters the wrong file name

9
Types of Errors

• Logical
• Not recognized by VB as wrong.
• No visible error produced by VB or your program
• These are the hardest to debug
• avg first_num second_num / 2

10
ANSI Characters

• About 47 keys on your keyboard
• Each key has two possible characters
• At least 94 different characters
• Each character is represented by a number
• Chr(n) - gives you character for n
• Asc(c) - gives you number n for c
• See Page 605 - Appendix A
• Also referred to as ASCII

11
ANSI Examples

• txtBox.Text Chr(65)
• This will display A in the txtBox

Why do I care? I could just do txtBox.Text A
12
ANSI Example

• Special Characters
• txtBox.Text 32 Chr(176) Fahrenheit
• This will display
• 32 Fahrenheit

13
Logic Conditions

• A condition is a expression that is either true
  or false
• Used in various VB statements (if, while, for,
  etc)
• Conditions contain
• Logical Operators
• Relational Operators
• Combination of both

14
Relational Operators

• Equal
• Not Equal
• ltgt
• Less Than
• lt
• Greater Than
• gt
• Less Than or Equal
• lt
• Greater Than or Equal
• gt

15
Example

• 1lt1
• 1lt1
• car lt cat
• Dog lt dog

16
Logical Operations

• Conditions can involve logical operations
• And
• Or
• Not
• (n lt 5) And (n gt 10)
• (n gt 5) Or (n lt 10)

17
Logical Operations

• Not - Flips a true to false and false to true
• 5 lt 4 is False
• Not 5 lt 4 evaluates to True
• And - Results in True if both are True, but False
  otherwise
• (5 lt 4) And (5 5) is False
• (4 lt 5) And (5 5) is True

18
Logical Operations

• Or - Results in False only if both are False,
  True otherwise
• (5 lt 4) Or (5 5) is True
• (4 lt 5) Or (5 ltgt 5) is True
• (5 lt 4) Or (5 ltgt 5) is False

19
Logical Operations

• Evaluated left to right
• Not takes precedence over And and Or
• And takes precedence over Or
• And and Or take something on both sides
• Not takes only a single thing
• Not legal xltyltz
• Legal xlty And yltz

20
More Examples

• Let n 4
• n lt 6 And Not (n 4)
• (n gt 100) Or (n lt 90)
• Let answ Y
• answ y
• Not (answ Y)
• (n lt 6) And (answ Y)

21
Boolean Data Type

• Boolean is another variable type
• Used to store outcomes for conditions, so only
  stores true or false
• Dim b as Boolean
• b x lt y

22
Types of Operations

• Arithmetic operations first
• Relational operations next
• Logical operations last

23
Logical Operations

• Not (x 5)
• is the same as
• x ltgt 5
• x lt 5 is not the opposite of x gt 5 - Why?
• Is xlt 5 the opposite of x gt 5?

24
Decisions

• So far we have just told the computer what to do
  in the order we want it to do it
• BUT what if we want it to do something if some
  condition is meet?
• If and Select Case statements will be used

25
If Blocks

• If condition_1 Then
• block_1
• ElseIf condition_2
• block_2
• Else
• block_3
• End If

26
If Blocks

• If condition_1 Then
• block_1
• ElseIf condition_2
• block_2
• Else
• block_3
• End If

executed ONLY if condition_1 is true
27
If Blocks

• If condition_1 Then
• block_1
• ElseIf condition_2
• block_2
• Else
• block_3
• End If

executed ONLY if condition_1 is false AND
condition_2 is true
28
If Blocks

• If condition_1 Then
• block_1
• ElseIf condition_2
• block_2
• Else
• block_3
• End If

executed ONLY if condition_1 is false AND
condition_2 is false
29
If Blocks

• If condition_1 Then
• block_1
• ElseIf condition_2
• block_2
• Else
• block_3
• End If

Any Code After End If will be executed regardless
of the conditions
More Code
30
If Blocks

• ElseIf is optional, this is totally fine
• If condition_1 Then
• block_1
• Else
• block_3
• End If

31
If Blocks

• Else is also optional, this is totally fine
• If condition_1 Then
• block_1
• ElseIf condition_2
• block_2
• End If
• Or
• If condition_1 Then
• block_1
• End If

32
Nested If Blocks

• Nesting refers to having one block inside another
  block
• If cond1 Then
• If cond2 Then
• block1
• End If
• End If

33
Nested If Blocks

• These can be confusing
• A better way of writing the previous example is
• If cond1 And cond2 Then
• block1
• End If

34
Code Example

• Profit/Loss
• Accept input of Costs and Revenue and have a
  button to calculate the Profit or Loss. Display
  one or the other
• Loss is xxxx.xx
• Or
• Profit is xxxx.xx