1. EGR 141 Computer Problem Solving in Engineering and Computer Science
IF and CASE

2. Decisions If condition Then ‘ statement(s) End If
True
False
Steps to process
if condition is
true
If condition Then ‘ statement(s) End If
If condition Then ‘ statement(s) for true Else ‘ statement(s) for false End If
Condition ?
True
False
Steps to process
if condition is
true
false

3. Decisions

4. Decisions

5. Decisions Check the invalid cases in the condition
Make sure that salary is between $500 and $2500:
If Not (Salary >= 500 And Salary <= 2500) Then
‘ do error processing since outside range limits
End If
is equivalent to
If Salary < 500 Or Salary > 2500 Then

6. Decisions Check the invalid cases in the condition
Make sure that age is between 21 and 75:
If CInt(txtAge.Text) < 21 OR _
CInt(txtAge.Text) > 75 Then
‘ do error processing since outside range limits
End If
Make sure single people have no spouse
If txtStatus.Text = “single” AND
txtSpouse.Text <> “” Then
‘ do error processing - spouse given for single person

7. Decisions If condition1 Then Statements for steps ABC
statement(s) for condition1 and condition2 true
Else
statement(s) for condition1 true and condition2 false
End If
Statements for steps XYZ
statement(s) for condition1 false
Condition1 ?
False
True
Steps to process if condition 1 is false
Condition2 ?
Steps to process if condition1 is true and condition2 is false
Steps to process if both condition1 and condition2 are true
Steps ABC
Steps XYZ
Note the indentation

8. Decisions IF… THEN ELSEIF… THEN If condition1 Then If condition1 Then
Statements for steps ABC
End If
If condition2 Then
Statements for steps DEF
If condition3 Then
Statements for steps GHI
If condition4 Then
Statements for steps JKL
Statements for steps XYZ
Else
statement(s) for condition1 false
If condition1 Then
Statements for steps ABC
ElseIf condition2 Then
Statements for steps DEF
ElseIf condition3 Then
Statements for steps GHI
ElseIf condition4 Then
Statements for steps JKL
Statements for steps XYZ
Else
statement(s) for condition1 false
End If
IF… THEN
ELSEIF… THEN

9. Decisions Note the indentation Select Case expression Case cond1
True
False
Steps to process if cond1 True
Case expression
cond2
Steps to process if cond2 True
condn
Steps to process if condn True
Steps to process if condn False
When every decision in nested if compares values against the same expression
Select Case expression
Case cond1
statement(s) for cond1 true
Case cond2
statement(s) for cond1 false and cond2 true :
Case condn
statement(s) for cond1-condn-1 false and condn true
Case Else
statement(s) for al conditions false
End Select
Note the indentation