pemrograman1 3 expressions forloops

7/27/2019 Pemrograman1 3 Expressions Forloops

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Copyright 2010 by Pearson Education1

Building Java Programs

Chapter 2

Lecture 3: Variables, For Loops, Nested Loops

reading: 2.2 2.3

(Slides adapted from Stuart Reges, Hlne Martin,and Marty Stepp)


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Variablesreading: 2.2


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Receipt example

Apakah yg kurang tepat /jelek, pada kode berikut?public class Receipt {

public static void main(String[] args) {// Calculate total owed, assuming 8% tax / 15% tipSystem.out.print("Subtotal: ");System.out.println(38 + 40 + 30);

System.out.print("Tax: ");System.out.println((38 + 40 + 30) * .08);System.out.print("Tip: ");System.out.println((38 + 40 + 30) * .15);System.out.print("Total: ");System.out.println(38 + 40 + 30 +

(38 + 40 + 30) * .08 +(38 + 40 + 30) * .15);}

}

Ekspresi subtotal (38 + 40 + 30) berulang /tdk efisien

Terlalu banyak statement println


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Variables

variable: satu unit memory komputer yang diberi namadan tipe yang dapat menyimpan satu nilai tertentu.

Seperti pengingat stasion radio pada audio mobil, atau

pengingat nomor phoneBook pada Hp:

Langkah-langkah untuk memakai variabel dlm program:

Mendeklarasikan - memasang /memberi nama and tipe

Menginisialisasi - memberi nilai awal

Menggunakan - cetak / memakainya dalam perhitungan


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Declaration

variable declaration: Memesan satu lokasi di memory untukmenyimpan satu nilai.

Variabel-variabel harus dideklarasikan dahulu sebelum dapatdigunakan.

Syntax:

typename; Nama adalah sebuahidentifier.

int zipcode;

int kodePos

double myGPA;

double indeksPrestasiKu

zipcode

myGPA


7/47Copyright 2010 by Pearson Education

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Assignment

assignment: Penugasan / adalah menyimpan ataumemberi nilai ke dalam sebuah variabel.

Nilai boleh dalam bentu ekspresi; variabel menyimpan hasilekspresinya.

Syntax:

name = expression;

int zipcode;zipcode = 90210; //literal = ekspresi simple

double myGPA;

myGPA = 1.0 + 2.25; //ekspresi

zipcode 90210

myGPA 3.25


8/47Copyright 2010 by Pearson Education8

Menggunakan variabel

Setelah diberi nilai, variabel dpt digunakan dlm ekspresi:int x;

x = 3;

System.out.println("x is " + x); // x is 3

System.out.println(5 * x - 1); // 5 * 3 - 1

Anda dapat memberi nilai ke sebuah

Variabel berkali-kali sesuai kebutuhan:

int x;x = 3;

System.out.println(x + " here"); // 3 here

x = 4 + 7;

System.out.println("now x is " + x); // now x is 11

x 3x 11



Deklarasi/inisialisasi

Sebuah variabel dapat di deklarasikan /di-inisialisasikandalam sebuah statement tunggal.

Syntax:

typename = value;

double myGPA = 3.95;

int x = (11 % 3) + 12;x 14

myGPA 3.95



Assignment and algebra

Assignment memakai tanda = , tetapi ini tidak samadengan persamaan pada matematika aljabar.

tanda= berarti, simpan nilai di kanan tanda = ke dalamvariabel di kiri tanda ="

Eksprsi di sebelah kanan di evaluasi terlebih dahulu,

kemudian hasilnya disimpan ke variabel sebelah kiri.

Apakah yang terjadi pada ekspresi di bawah ini?int x = 3;

x = x + 2; // ??? x 3x 5



Increment dan decrement

shortcuts untuk menambah atau mengurangi sebuah variabledengan nilai 1

ekspresi pendek sama dg ekspresi panjangvariable++; variable = variable + 1;

variable--; variable = variable - 1;

int x = 2;

x++; // x = x + 1;

// x now stores 3double gpa = 2.5;

gpa--; // gpa = gpa - 1;

// gpa now stores 1.5



Operator Modify-dan-assign

shortcuts untuk memodifikasi nilai variabel

Ekspresi pendek Equivalent ekspresi panjangvariable += value; variable = variable + value;

variable -= value; variable = variable - value;

variable *= value; variable = variable * value;variable /= value; variable = variable / value;

variable %= value; variable = variable % value;

x += 3; // x = x + 3;gpa -= 0.5; // gpa = gpa - 0.5;

number *= 2; // number = number * 2;



Assignment dan tipe data

Sebuah variabele hanya dapat menyimpan nilai sesuaidenga tipenya.

int x = 2.5; // ERROR: incompatible types

Nilai int dapat disimpan ke dalam variabel double. The value is converted into the equivalent real number.

double myGPA = 4;

double avg = 11 / 2;

Mengapakah avg menyimpan 5.0bukan 5.5 ?

myGPA 4.0

avg 5.0



Kesalahan kompilasi

Sebuah variabel tidak dapat di pakai sampai kepadanyadiberi satu nilai tertentu.

int x;

System.out.println(x); // ERROR: x has no value

Jangan mendeklarasikan variabel yang sama 2 kali.

int x;int x; // ERROR: x already exists

int x = 3;

int x = 5; // ERROR: x already exists

Bagaimana perbaikan untuk kode di atas?



Mencetak nilai sebuah variabel

Gunakan tanda + untuk mencetak String dan nilai sebuahvariabel secara langsung dalam satu baris.

double IP = (95.1 + 71.9 + 82.6) / 3.0;

System.out.println(IP anda adalah " + IP);

int mhs = 11 + 17 + 4 + 19 + 14;

System.out.println(Terdapat " + mhs +

" mahasiswa dalam kuliah ini.");

Output:

IP anda adalah 83.2

Terdapat 65 mahasiswa dalam kuliah ini.



Receipt question

Ubahlah program berikut dg menggunakan variabel.public class Receipt {

public static void main(String[] args) {// Calculate total owed, assuming 8% tax / 15% tipSystem.out.print("Subtotal: ");System.out.println(38 + 40 + 30);

System.out.print("Tax: ");System.out.println((38 + 40 + 30) * .08);

System.out.print("Tip: ");System.out.println((38 + 40 + 30) * .15);

System.out.print("Total: ");System.out.println(38 + 40 + 30 +

(38 + 40 + 30) * .15 +(38 + 40 + 30) * .08);

}

}



Jawaban program

public class Receipt {public static void main(String[] args) {// Calculate total owed, assuming 8% tax / 15% tipint subtotal = 38 + 40 + 30;double tax = subtotal * .08;double tip = subtotal * .15;double total = subtotal + tax + tip;

System.out.println("Subtotal: " + subtotal);System.out.println("Tax: " + tax);System.out.println("Tip: " + tip);System.out.println("Total: " + total);

}

}



Building Java Programs

Chapter 2Lecture 2-2: The for Loop

reading: 2.3



Repetition with for loops

Sejauh ini, aksi berulang menghasilokan kode redudansi:makeBatter();

bakeCookies();

bakeCookies();

bakeCookies();

bakeCookies();

bakeCookies();

frostCookies();

Statement for loop dalam java memfasilitasi perulangantask /tugas.

mixBatter();

for (int i = 1; i



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for loop syntax

for (initialization; test; update) {statement;

statement;

...

statement;

}

Inisialisasi /initialization hanya dilakukan satu kali saja.

Yang diulangi adalah hal-hal berikut:

Periksa apakah nilai kondisi pengujian/ test bernilai benar. Jika

nilai kondisi pengujian selah, hentikan perulangan.

Eksekusi statement- statement

Lakukan update.

body

header



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Control structures

Struktur kendali /Control structure: pemrograman adalahsuatu konstruksi yang berdampak pada aliran eksekusiprogram.

Kode-kode yang dikendalikan bisa satu statement ataulebih

Struktur for loop adalah sebuah contoh dari sebuahstruktur pengendalian perulangan /looping.



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Inisialisai /Initializationfor (

int i = 1; i



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Testfor (int i = 1;

i = Lebih besar dari atau samadengan /greater than or

equal to

== Sama dengan /exactly equal to

!= Tidak samadengan /not equal to



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Update

for (int i = 1; i


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Repetition over a rangeSystem.out.println("1 squared = " + 1 * 1);System.out.println("2 squared = " + 2 * 2);System.out.println("3 squared = " + 3 * 3);System.out.println("4 squared = " + 4 * 4);System.out.println("5 squared = " + 5 * 5);System.out.println("6 squared = " + 6 * 6);

Intuition: "I want to print a line for each number from 1 to 6"

The for loop does exactly that!

for (int i = 1; i


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Loop walkthrough

for (int i = 1; i


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Multi-line loop bodySystem.out.println("+----+");

for (int i = 1; i


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Expressions for counter

int highTemp = 5;for (int i = -3; i


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System.out.print

Prints without moving to a new line allows you to print partial messages on the same line

int highestTemp = 5;

for (int i = -3; i


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Counting down

The update can use -- to make the loop count down. The test must say > instead of= 1; i--) {

System.out.print(i + ", ");}

System.out.println("blastoff!");

System.out.println("The end.");

Output:T-minus 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, blastoff!

The end.


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Nested loopsreading: 2.3


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Nested loops

nested loop: perulangan yang terletak pada perulanganlainnya.

for (int i = 1; i


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Nested for loop exercise

Apakah hasil dari perulangan for dibawah ini?for (int i = 1; i


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Apakah hasil dari perulangan for dibawah ini?for (int i = 1; i


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Common errors

Both of the following sets of code produce infinite loops:for (int i = 1; i


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Complex lines

What nested for loops produce the following output?

....1

...2

..3

.4

5

We must build multiple complex lines of output using: an outer "vertical" loop for each of the lines

inner "horizontal" loop(s) for the patterns within each line

outer loop (loops 5 times because there are 5 lines)

inner loop (repeated characters on each line)


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Outer and inner loop

First write the outer loop, from 1 to the number of lines.for (int line = 1; line


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Mapping loops to numbersfor (int count = 1; count


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Loop tables

What statement in the body would cause the loop to print:2 7 12 17 22

To see patterns, make a table ofcount and the numbers.

Each time count goes up by 1, the number should go up by 5.

But count * 5 is too great by 3, so we subtract 3.

count number to print 5 * count

1 2 5

2 7 103 12 15

4 17 20

5 22 25

5 * count - 3

2

712

17

22


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Loop tables question

What statement in the body would cause the loop to print:17 13 9 5 1

Let's create the loop table together. Each time count goes up 1, the number printed should ...

But this multiple is off by a margin of ...

count number to print

1 17

2 133 9

4 5

5 1

-4 * count -4 * count + 21

-4 17

-8 13-12 9

-16 5

-20 1

-4 * count

-4

-8-12

-16

-20


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Another view: Slope-intercept

The next three slides present the mathematical basis forthe loop tables. Feel free to skip it.

-10

-5

0

5

10

15

20

25

-2 0 2 4 6

count (x) number to print (y)

1 2

2 7

3 12

4 17

5 22


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Another view: Slope-intercept Caution: This is algebra, not assignment!

Recall: slope-intercept form (y = mx + b)

Slope is defined as rise over run (i.e. rise / run). Since the run isalways 1 (we increment along x by 1), we just need to look at therise. The rise is the difference between the y values. Thus, the

slope (m) is the difference between y values; in this case, it is +5.

To compute the y-intercept (b), plug in the value ofy at x = 1 andsolve for b. In this case, y = 2.

y = m * x + b

2 = 5 * 1 + b

Then b = -3

So the equation isy = m * x + b

y = 5 * x 3

y = 5 * count - 3

count (x) number to print (y)

1 2

2 7

3 12

4 17

5 22


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Another view: Slope-intercept

Algebraically, if we always take the value ofy atx = 1, then we can solve for b as follows:y = m * x + b

y1 = m * 1 + b

y1 = m + b

b = y1m

In other words, to get the y-intercept, just subtractthe slope from the first y value (b = 2 5 = -3) This gets us the equation

y = m * x + by = 5 * x 3

y = 5 * count 3

(which is exactly the equation from the previous slides)


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Make a table to represent any patterns on each line.....1

...2

..3

.4

5

To print a character multiple times, use a for loop.

for (int j = 1; j


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Nested for loop solution

Answer:for (int line = 1; line


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What is the output of the following nested for loops?for (int line = 1; line


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Modify the previous code to produce this output:....1...2.

..3..

.4...

5....

Answer:for (int line = 1; line

pemrograman1 3 expressions forloops

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