Matakuliah
Tahun
Versi
: D0524 / Algoritma dan Pemrograman Komputer
: 2005
:
Pertemuan 05
Selection
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Mendemonstrasikan penggunaan perintah
seleksi
2
Outline Materi
• The If…Then...Else Statement
• Nested If Statement
• The Select Case Statement
3
The If…Then...Else Statement
• The If…Then…Else statement enables a program to
handle situations having two outcomes.
• The statement has three parts:
1.The condition.
2.The statements to perform for the first outcome.
3.The statements to perform for the second outcome.
• Syntax and Action of If…Then…Else
– The If…Then…Else statement has the following syntax:
• If condition Then
– Statementblock1
• Else
– Statementblock2
• End If
4
The If…Then...Else Statement
– Run Time: The Effect of the If…Then…Else
Statement
• True: the computer executes the statements in
statementblock1.
• False: the computer skips to Else and executes the
statements in statementblock2.
– Meta Statements
• Describe compound statement with a single phrase.
– Problem Solving and Pseudocode
• Problem solving is the process of writing code to perform a
required task.
• Pseudocode is an English-like outline of the logical for
program code.
– Ex. Request address from user
Receive input in a textbox
5
The If…Then...Else Statement
– Using Logical Expressions in If…Then…Else
Statements
• The condition of an If…Then…Else statement may
be a logical expression.
– Ex. (YearsExperience>5) And (NumberOfLanguages>=3)
– If…Then
• Sometimes only one of two outcomes requires
processing.
– If condition Then
statementblock
– End If
6
Nested If Statement
• If statements may contain one within
another.
If (X<Y) And (Y<Z) Then
AscOrDesc = “ascending”
Else
If (X>Y) And (Y>Z) Then
AscOrDesc = “descending”
Else
AscOrDesc = “neither ascending nor descending”
End If
End If
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The Select Case Statement
• Can handle conditions with multiple outcomes.
– Syntax and Action of Select Case
Select Case testexpression
Case expressionlist1
statementblock1
Case expressionlist2
statementblock2
…
Case expressionlistN
statementblockN
Case Else
statementblock
End Select
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The Select Case Statement
– Run Time: The Effect of the Select Case Statement
•
•
•
•
•
•
•
First the computer evaluates the test expression.
Then it tries to match the resulting value.
The search starts at the top expression list.
The computer stops at the first match.
The corresponding statement block is executed.
Control resumes after the End Select.
If no match occurs and a Case Else exists, then the Case Else
block is executed.
• Then control resumes after the End Select.
• If no match occurs and no Case Else exists, then control resumes
after the End Select.
– Ranges
• Two variations
– Use the keyword “To”
» Ex. 25 To 37
– Use the keyword “Is”
» Ex. Is >= 77
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If versus Select Case
• If a decision has only two outcomes and the condition
can be expressed as a single logical expression, then
the If statement is easier to read.
• If a decision has multiple outcomes that depend on a
single expression, then the Select Case is usually easier
to read.
• If the outcomes depend on a number of conditions that
may be independent, then embedded If statements are
better.
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