1. VB Decisions, Conditions & If
Chapter 5.1 & 5.2
12/30/2018
Prepared By: Deborah Becker

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Covered Tipics
Relational & Logical Operators
Using And, Or, and Not
If Blocks
Read & Create Flowcharts (Logic)
12/30/2018
Prepared By: Deborah Becker

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A Condition
Definition
Condition is an expression involving relational operators (such as > or =) that is either true or false.
Example:
“Frog” = “Frog”
12 > 8 =
12/30/2018
Prepared By: Deborah Becker

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Conditions
> greater than
< less than
= equal to
<> not equal to
>= greater than or equal to
<= less than or equal to
12/30/2018
Prepared By: Deborah Becker

5. Mathematical Relational Operators
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Prepared By: Deborah Becker

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Is the Condition True?
1 <= 1
1 < 1
“car” < “cat”
“Dog” < “dog”
2. False < means less than. No number can be less than itself
True Characters of a string are compared one at a time, working from left to right. The first two characters match and the third decides if the condition is true. R precedes T in the alphabet.
True Uppercase letters precede lowercase letters in the ANSI table.
12/30/2018
Prepared By: Deborah Becker

7. Are These Conditions True?
Let a = 4 and b = 3
Let c = “hello” and d = “bye”
(a + b) < (2 * a)
(Len(c) – b) = (a / 2)
C < (“good” & d)
1. True = 7 and 2 * 4 = 8
2. True Len(c) = 5 – 3 = 2 and (4 / 2) = 2
False H follows G in the ANSI table
12/30/2018
Prepared By: Deborah Becker

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Logical Operators
The three main logical operators are
And Or
Not
Some programming conditions require more complicated comparison then just true or false
12/30/2018
Prepared By: Deborah Becker

9. Logical Operators allow us to..
Evaluate condition1 and condition2 based on the following
condition1 and condition2
condition1 or condition2
condition1 not condition2
12/30/2018
Prepared By: Deborah Becker

10. Are these conditions T/F?
Dim answ as String = “Y”
(answ = “Y”) or (answ = “y”)
(answ = “Y”) and (answ = “y”)
Not (answ = “y”)
True the condition become “Y” = “Y”
False the condition would be false for every condition fo answ. You can not set a variable = to two separate values simultaneously
True because “Y” = “y” is false
12/30/2018
Prepared By: Deborah Becker

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Using Parentheses
Using parentheses can improve readability.
Place parentheses in this equation to help evaluate it.
a < b + c OR d < e AND f = g
12/30/2018
Prepared By: Deborah Becker

12. Is this easier to understand?
((a < (b + c)) Or ((d < c) And (F = g))
A condition involving numeric variables is different from an algebraic truth.
The condition (a + b) < 2 * a is not a valid algebraic truth because it is not true for all values of a and b
VB will evaluate it as true if it is correct for the current values of the variables
12/30/2018
Prepared By: Deborah Becker

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The IF Statements
If School Day
False
True
Stay In Bed
Go to Class
Action
Action
The if block allows a program to decide on a course of action.
In the If statement You are always testing the condition to determine if it is True or False
If no Else statement is included then the statement is only executed if the condition is true.
12/30/2018
Prepared By: Deborah Becker

14. If Statement Examples in VB
If … Then (all on one line)
If strName = "Jamie" Then lblMessage.text = "Hello Jamie"
Block If … Then … End If If strName = "Sam" Then
lblMessage.text = "Hello Sam" login(strName)
End If
In the If Statement, when the condition is true, the Then clause is executed; when the condition is false, only the Else clause, if present, is executed.
The if block must contain an End If. It is always two words
Time
12/30/2018
Prepared By: Deborah Becker

15. Block If…Then…Else…End If
If strName = "Connie" Then
lblMessage.text = "Hello Connie" Login(strName)
Else
lblMessage.text = "Hello”
msgbox(“Not a valid User”)
End If
The if then else clause can contain an else condition
If today is cloudy then
go to class
Else
go to beach
End if
12/30/2018
Prepared By: Deborah Becker

16. If…then…ElseIf…then…end if
If School Day
True
False
If Sunny
Stay In Bed
False
True
Play Tennis
Go to Class
12/30/2018
Prepared By: Deborah Becker

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Example
If costs = revenue Then
lblResult.text = “Break even”
ElseIf costs < revenue Then
profit = revenue – costs
lblResult.text = “Profit is “; _ FormatCurrency(profit)
Else loss = costs – revenue
lblResult.text = “Loss is “; _ FormatCurrency(loss)
End if
Elseif is written as one word
End if is always two words.
12/30/2018
Prepared By: Deborah Becker

18. If Block and Logic Operators
The If Block can be combined with logic operators to compare more than one condition
If (answer >= .5) and (answer <= 1) Then
lblSolution.text = “true”;
Else
lblSolution.text = “false”
End if
12/30/2018
Prepared By: Deborah Becker

19. Nesting Ifs—MultipleValidations
If you needed to check several input fields using nested ifs can eliminate the need to display multiple message statements
Error messages are only displayed for the conditions that are false (Else)
12/30/2018
Prepared By: Deborah Becker

20. Additional Information
It is not necessary to indent If Blocks
We indent to improve readability
When constructs contain If Blocks inside other If Blocks, they are referred to as Nested Ifs
Some times the use of relational operators can simplify the If Block structure making it easier to understand
If condition1 Then
If condition2 Then
action
End if
If condition1 and condition2 then
12/30/2018
Prepared By: Deborah Becker

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How can we simplify
If condition1 Then
If condition2 Then
action
End if
If condition1 and condition2 then
action
End if
12/30/2018
Prepared By: Deborah Becker

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Flowcharting the Ifs
Flowcharts are a good tool to evaluate If Blocks
We will use some example problems to see how flowcharting can add clarification to analyzing a problem
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Prepared By: Deborah Becker

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The Problem
In New Jersey the state income tax is based on a persons base income at three different interval levels
The tax on Income <= $20,000 is taxed at 2% of income
The tax on Income > $20,000 but <= $50,000 is $400 plus 2.5% of (income -$20,000)
The tax on income > $50,000 is $1150 plus 3.5% of (income - $50,000)
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Prepared By: Deborah Becker

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The End
That’s All Folks
12/30/2018
Prepared By: Deborah Becker