Transcript PERCABANGAN Bagaimana Jika YA? Bagaimana Jika TIDAK? Bagaimana Jika BENAR?

PERCABANGAN
Bagaimana Jika YA?
Bagaimana Jika TIDAK?
Bagaimana Jika BENAR?
Bagaimana jika SALAH?
Catch-up Exercise
• Buat program java untuk menghitung
luas segi tiga.
• Tes program dengan input:
• Alas = 20, tinggi = 10
• Alas = 10, tinggi = -30
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Flow of Control
• Flow of Control
Cara kerja komputer memproses perintah
dalam sebuah program:
– Sequentially; baris per baris,
– Conditionally; dengan perintah percabangan
– Repetitively; menggunakan perintah perulangan
• Program yang selama ini dibuat adalah
sekuensial.
• Dalam slide ini akan dibahas jenis Kondisional.
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Perintah Seleksi
• Selection or branching statement
menentukan the action that should be
taken by the computer.
• Titik dimana a decision has to be made as
to jalur yang akan diambil.
yes
<buy a house>
<buy a car>
<give to charity>
IF <Saya punya uang 1 M>
no
no
<ambil kredit>
<baik ke semua orang>
<perbanyak doa>
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Perintah if-else
• In Java, we can write a selection statement
using if-else
• Syntax:
if <ekspresi boolean >
<statement_1>
else
<statement_2>
• Jika ekspresi boolean bernilai true, maka
statement_1 yang akan dieksekusi.
• Jika ekspresi boolean bernilai false, maka
statement_2 yang akan dieksekusi.
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Example 1
•
•
•
•
Perhatikan fragmen program berikut ini:
int age;
Scanner keyboard = new Scanner (System.in);
age = keyboard.nextInt();
if (age < 21)
System.out.println("too young to vote");
else
System.out.println("register as voter");
• What is the output if the user enters
– 16
– 23
– 21
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Example 2
count = 4;
total = 5;
if (count < 3)
total = 0;
else
total = total + count;
System.out.println(total);
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Compound Statements
• To include multiple statements in a branch, enclose the
statements in braces.
if (count < 3)
{
total = 0;
count = 0;
}
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Menghilangkan Bagian else
• Jika bagian else dihapus and the expression
after the if is false, no action occurs.
• syntax
if (Boolean_Expression)
Statement
• example
weight = 50;
ideal = 60;
if (weight > ideal)
caloriesPerDay -= 500; //kalori = kalori-500;
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Ekspresi Boolean
• When processing a selection statement
such as an if statement, the computer must
evaluate a boolean expression.
• Recall the boolean primitive data type that
holds the value true or false.
• A boolean expression is sebuah ekspresi
yang menghasilkan nilai true or false.
• Boolean expressions biasanya memakai
operator perbandingan (also known as
relational operators)
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Operators Perbandingan
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Exercise [Latihan]
1. Write a Java program that asks the user
for a score and displays "You pass" if the
score is greater than or equal to 50 and
"You fail" otherwise.
2. Write a Java program that asks the user
for a grade and displays "Wow!" if the
grade is 'A' and "Try harder next time"
otherwise.
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Operator Logika
• Formula ekspresi boolean seringkali menjadi kompleks.
• Modifikasilah program sebelumnya, so that it will display
"You pass" if the assignment score is greater than or
equal to 50 DAN the examination score is greater than or
equal to 60.
• We will need to use operator logika for more complex
boolean expressions:
– && (and)
– || (or)
– ! (not)
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Truth Table/ Tabel Kebenaran
• Refer to the following truth table for logical
operators, assuming P and Q are boolean
expressions:
P
Q
P && Q
P || Q
!P
!Q
true
true
true
true
false
false
true
false
false
true
false
false
false
true
false
true
true
true
false
false
false
false
true
true
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Presedensi Operator
• We have looked at operator Arithmetic, operator
Relational and Operator Logical.
• Jika operators tersebut dipakai bersama dalam sebuah
expression, they must be evaluated menurut the
precedence rules:
–
–
–
–
–
–
–
Parentheses (or brackets)
Type cast
(type)
Logical not
!
Arithmetic * / % * / %
Arithmetic + –
+–
Relational operators
> >= < <= == !=
Logical AND and OR
&& ||
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Ekspresi Boolean Majemuk
• Boolean expressions can be combined using the
“or” (||) operator.
• example
if ((quantity > 5) || (cost < 10))
...
• syntax
(Sub_Expression_1)
|| (Sub_Expression_2)
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Compound Statements/
Perintah Majemuk
• When a list of statements is enclosed in braces
({}), they form a single compound statement.
• syntax
{
Statement_1;
Statement_2;
…
}
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Exercise
• Evaluate the following expressions
– (10 < 5) || (3 > 7)
– !true && false
– !(5==8)
– true || !false
– !(3 > 5 && 4 + 1 < 3 * 2) || 3 !=
3
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The if Statement
• We can also use if without else:
• Syntax:
– if <boolean expression>
<execute these statements>
• If more than one statement is to be
executed, they must be enclosed in curly
brackets:
if ((rich =='y') || (famous == 'y'))
{ System.out.println("I will be your friend");
System.out.println("You are either rich or famous");
}
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Indentation
• Important to improve the clarity of your
program.
• Show which statements are part of the if.
• However, remember that indents are
ignored by the compiler.
• What is the output of the following
program fragment for num = 8? num = 15?
if (num < 10)
num = num + 10;
System.out.println("num is " + num);
System.out.println("Finished!");
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Nested [bersarang] if
• We can nest an if (or if-else) statement inside
another if (or if-else) statement.
• Consider the following:
– Jika seorang mahasiswa adalah angkatan tahun 1,
maka nilai lulusnya adalah 50, jika mahasiswa
angkatan tahun 2, maka nilai lulusnya adalah 60 dan
untuk angkatan tahun 3, maka nilai lulusnya adalah
40.
• Write the code fragment to represent this.
• Remember, every else must have an if (but not
necessary vice-versa)
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if-else pairs
Example
if (year == 1)
if (mark >= 50)
System.out.println("You pass");
else
System.out.println("You fail");
else if (year == 2)
if (mark >= 60)
System.out.println("You pass");
else
System.out.println("You fail");
else if (year == 3)
if (mark >= 40)
System.out.println("You pass");
else
System.out.println("You fail");
else
System.out.println("Cannot be determined");
nested if-else
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Exercise
• Write a Java program that will ask the user
for a number and display the square root
of the number if it is positive.
– Use the Math.sqrt() method.
• Next modify the program so that if the user
enters a negative number, an error
message will be displayed.
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Exercise
• Write a Java program that asks the user
for his or her name and gender then
displays
"Hello Mr. xxx" or "Hello Ms. xxx" as
appropriate. If an invalid value is entered
for the gender, just return the name "xxx".
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Nested Statements
• An if-else statement can contain any sort of
statement within it.
• In particular, it can contain another if-else
statement.
– An if-else may be nested within the “if”
part.
– An if-else may be nested within the “else”
part.
– An if-else may be nested within both parts.
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Nested Statements, cont.
• Each else is paired with the nearest
unmatched if.
• If used properly, indentation
communicates which if goes with which
else.
• Braces can be used like parentheses to
group statements.
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Nested Statements, cont.
• syntax
if (Boolean_Expression_1)
if (Boolean_Expression_2)
Statement_1)
else
Statement_2)
else
if (Boolean_Expression_3)
Statement_3)
else
Statement_4);
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Multibranch if-else Statements
• syntax
if (Boolean_Expression_1)
Statement_1
else if (Boolean_Expression_2)
Statement_2
else if (Boolean_Expression_3)
Statement_3
else if …
else
Default_Statement
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Multibranch if-else Statements, cont.
• equivalent code
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The switch Statement
• The switch statement is a mutltiway branch that
makes a decision based on an integral (integer
or character) expression.
• The switch statement begins with the keyword
switch followed by an integral expression in
parentheses and called the controlling
expression.
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The switch Statement, cont.
• A list of cases follows, enclosed in braces.
• Each case consists of the keyword case
followed by
– a constant called the case label
– a colon
– a list of statements.
• The list is searched for a case label matching
the controlling expression.
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Switch Statement
• The switch statement is a branching statement that allows
multiple options.
• This is similar to using nested if-else statements but it is
simpler and often clearer.
switch (gender)
{
case 'm': case 'M':
System.out.println("Hello, Mr. " + name);
break;
case 'f': case 'F':
System.out.println("Hello, Ms. " + name);
break;
default:
System.out.println("Hello, " + name);
break;
}
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Syntax – switch
switch (variable / expression)
{
case label1:
statement;
If the value of the
break;
variable /expression
case label2:
matches the case
case label3:
label, the statements
statement;
following the label
statement;
will be executed
break;
until a break is
case label4: case label5:
reached.
statement;
break;
optional section to be
default:
executed if none of
statement;
the case labels match
break;
the variable /
}
expression
Must be of type
byte, short, int
or char ONLY
Case label:
•must be constant
value
•compatible type
to the variable/
expression
•cannot be
duplicated
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Exercise
• Write a Java program that displays the
following menu and allows the user to
choose one of the options given. Then
display the required nursery rhyme.
Choose the rhyme:
1. winkle twinkle little star
2. Humpty Dumpty
3. London Bridge
Your choice? 2
Humpty Dumpty sat on the wall
Humpty Dumpty had a great fall
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Java Character Set
• Java uses unicode to represents characters. Unicode uses
2 bytes (16 bits) and are thus capable of representing a total
of 65536 different symbols, but only half of these are used.
• The first 256 unicode characters are the same as the ASCII
characters.
• All characters (whether unicode or ASCII) are represented
using numerical code.
– The character '0' is represented by the numerical code of 48, '9' 
57, 'A'  65, 'a'  97, etc.
• The expressions below are true:
–
–
–
–
'3' < '9'
'3' > 9
'B' > '4'
'a' > 'A'
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Exercise
• Write a program that asks the user to enter two
grades, student1Grade and student2Grade.
• The grade must be a character from 'A' to 'F'. If
the grade for either student is lower than 'C' then
display 'Help required'.
• Then display whether student1 or student2 got
the better grade.
• Use methods in your program
• Plan carefully!
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