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Turtles and Loops - Introduction to Computing Using Java | CS 1110, Assignments of Computer Science

Cornell UniversityComputer Science

Material Type: Assignment; Class: Introduction to Computing Using Java; Subject: Computer Science; University: Cornell University; Term: Fall 2008;

Typology: Assignments

Pre 2010

Uploaded on 08/31/2009

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1!
1!
CS1110, 16 October 2008!
Two topics: Turtles; loops"
Start reading Sec. 2.3.8 and chapter 7 on loops. "
The lectures on the ProgramLive CD can be a big help.!
The next time someone rather casually use a number that
includes the word "billion", think about it. !
• A billion seconds ago was 1959. !
• A billion minutes ago Jesus was alive. !
• A billion hours ago our ancestors were living in the Stone
Age. !
• A billion days ago no creature walked the earth on two feet.!
• A billion dollars lasts 8 hours and 20 minutes at the rate our!
government spends it.!
2!
Function HSVtoRGB"
0 <= h < 360 (degrees)!
Hi = floor(h/60) % 6!
Wikipedia: !f = h/60 – floor(h/60)!
A4 handout: !f = h/60 – Hi!
0 <= h < 360 !
=> !<arithmetic>!
0 <= h/60 < 6 !
=> !<arithmetic>!
floor(h/60) is in 0..5!
=> !<arithmetic>!
floor(h/60) = floor(h/60) % 6 !
=> !<definition of Hi>!
Wikipedia formula for f = A4 handout for f!
In fact, we and Wikipedia
could write Hi as !
Hi = floor(h/60) !!!! !
3!
Graphical User Interfaces (GUIs): graphics.!
A JFrame, with a "panel"
on which you can draw!
jframe= new JFrame("Turtle window");!
jpanel= new JPanel();!
jpanel.setPreferredSize(new Dimension(width, height));
jpanel.setBackground(Color.white);
jframe.getContentPane().add(panel, BorderLayout.CENTER);
jframe.pack(); !
jframe.setVisible(true);!
graphics= jpanel.getGraphics();!
A “panel” in which
you can draw!
You don’t have to learn
all this unless you want
to. We will be telling
you more and more
about GUIs as the
course progresses."
4!
Commands to draw!
// Draw line from (10, 10) to (50, 40).!
d.graphics.drawLine(10,10,50, 40);!
// Draw rectangle: top-left point (2, 5), width 40, height 60!
d.graphics.drawRect(2, 5, 40, 60);!
// Fill rectangle: top-left point (50, 70), width 40, height 60!
d.graphics.fillRect(50, 70, 40, 60);!
(0,0) (0,1) (0, 2) …!
(1,0) (1,1), (1,2) …!
(2,0) (2,1), (2,2) …!
…!
The panel: each pair (i,j) is a
“pixel” or picture element. !
d.graphics contains an
object of class Graphics.
It contains the methods to
draw on the panel!
5!
// Draw string s at (40, 30)!
d.graphics.drawString(s, 40, 30);!
// set the pen color to red!
d.graphics.setColor(Color.red);!
// Store the current color in c!
Color c= d.graphics.getColor();!
// Draw oval: top-left point (2, 5), width 40, height 60!
d.graphics.drawRect(2, 5, 40, 60);!
// Fill an oval: top-left point (50, 70), width 40, height 60!
d.graphics.fillRect(50, 70, 40, 60);!
(0,0) (0,1) (0, 2) …!
(1,0) (1,1), (1,2) …!
(2,0) (2,1), (2,2) …!
…!
For more on graphics, see class Graphics in the Java API and page
1-5 in the CD ProgramLive. For more on GUIs, read chapter 17 -
-corresponding part of the CD is much easier!!
6!
In A5, write methods
to draw shapes, draw
spirals, make balls
that move and
bounce off the sides
of the window, and
draw things using
recursive procedures. !
Assignment A5: drawing with a Turtle!
We have written a class Turtle, an instance of which maintains:!
•  point (x, y): where the “Turtle” is!
•  angle: the direction the Turtle faces !
•  a pen color!
•  whether pen is up or down!
Class Turtle has methods for moving a
Turtle around, drawing as it goes.!
Draw equilateral triangle with side
lengths 30; turtle ends up at starting
point and facing the same direction:!
forward(30); addAngle(120);!
forward(30); addAngle(120);!
forward(30); addAngle(120);!
0 degrees!
90 degrees!
180 degrees!
270 degrees!
pf3
pf4

Partial preview of the text

Download Turtles and Loops - Introduction to Computing Using Java | CS 1110 and more Assignments Computer Science in PDF only on Docsity!

1

CS1110, 16 October 2008

Two topics: Turtles; loops

Start reading Sec. 2.3.8 and chapter 7 on loops. 

The lectures on the ProgramLive CD can be a big help.

The next time someone rather casually use a number that

includes the word "billion", think about it.

  • A billion seconds ago was 1959.
  • A billion minutes ago Jesus was alive.
  • A billion hours ago our ancestors were living in the Stone

Age.

  • A billion days ago no creature walked the earth on two feet.
  • A billion dollars lasts 8 hours and 20 minutes at the rate our

government spends it. (^2)

Function HSVtoRGB 0 <= h < 360 (degrees)

Hi = floor(h/60) % 6

Wikipedia: f = h/60 – floor(h/60)

A4 handout: f = h/60 – Hi

0 <= h < 360

=>

0 <= h/60 < 6

=>

floor(h/60) is in 0..

=>

floor(h/60) = floor(h/60) % 6

=>

Wikipedia formula for f = A4 handout for f

In fact, we and Wikipedia

could write Hi as

Hi = floor(h/60) !!!!

3

Graphical User Interfaces (GUIs): graphics.

A JFrame, with a "panel"

on which you can draw

jframe= new JFrame("Turtle window");

jpanel= new JPanel();

jpanel.setPreferredSize(new Dimension(width, height));

jpanel.setBackground(Color.white);

jframe.getContentPane().add(panel, BorderLayout.CENTER);

jframe.pack();

jframe.setVisible( true );

graphics= jpanel.getGraphics();

A “panel” in which

you can draw

You don’t have to learn

all this unless you want

to. We will be telling

you more and more

about GUIs as the

course progresses.

4

Commands to draw

// Draw line from (10, 10) to (50, 40).

d.graphics.drawLine(10,10,50, 40);

// Draw rectangle: top-left point (2, 5), width 40, height 60

d.graphics.drawRect(2, 5, 40, 60);

// Fill rectangle: top-left point (50, 70), width 40, height 60

d.graphics.fillRect(50, 70, 40, 60);

The panel: each pair (i,j) is a

“pixel” or picture element.

d.graphics contains an

object of class Graphics.

It contains the methods to

draw on the panel

5

// Draw string s at (40, 30)

d.graphics.drawString(s, 40, 30);

// set the pen color to red

d.graphics.setColor(Color.red);

// Store the current color in c

Color c= d.graphics.getColor();

// Draw oval: top-left point (2, 5), width 40, height 60

d.graphics.drawRect(2, 5, 40, 60);

// Fill an oval: top-left point (50, 70), width 40, height 60

d.graphics.fillRect(50, 70, 40, 60);

For more on graphics, see class Graphics in the Java API and page

1-5 in the CD ProgramLive. For more on GUIs, read chapter 17 -

-corresponding part of the CD is much easier!

6

In A5, write methods

to draw shapes, draw

spirals, make balls

that move and

bounce off the sides

of the window, and

draw things using

recursive procedures.

Assignment A5: drawing with a Turtle

We have written a class Turtle, an instance of which maintains:

  • point (x, y): where the “Turtle” is
  • angle: the direction the Turtle faces
  • a pen color
  • whether pen is up or down

Class Turtle has methods for moving a

Turtle around, drawing as it goes.

Draw equilateral triangle with side

lengths 30; turtle ends up at starting

point and facing the same direction:

forward(30); addAngle(120);

forward(30); addAngle(120);

forward(30); addAngle(120);

0 degrees

90 degrees

180 degrees

270 degrees

7

The for loop, for processing a range of integers

x= 0;

// add the squares of int s

// in range 2..200 to x

x= x + 2*2;

x= x + 3*3;

x= x + 200;

repetend : the thing to be repeated.

The block:

{ x= x + i*i; }

for each number i in

the range 2..200,

add i*i to x.

The for-loop:

for ( int i= 2; i <= 200; i= i +1) {

x= x + i*i;

loop counter : i

initialization : int i= 2;

loop condition : i <= 200;

increment : i= i + 1

repetend or body : { x= x + i*i; }

8

Execution of the for-loop

The for-loop:

for ( int i= 2; i <= 4; i= i +1) {

x= x + i*i;

loop counter : i

initialization : int i= 2;

loop condition : i <= 4;

increment : i= i + 1

repetend or body : { x= x + i; }

Called a “flow chart”

To execute the for-loop.

  1. Execute initialization.
  2. If loop condition false,

terminate execution.

  1. Execute repetend.
  2. Execute increment,

repeat from step 2.

i= 2;

i <= 4

i= i +1;

true

false

x= x + i*i;

9

Execution of the for-loop

x= 1;

for ( int i= 1; i <= 4; i= i +1) {

x= 2*x;

Called a “flow chart”

i= 2;

i <= 4

i= i +1;

true

false

x= x + i*i;

At the end:

A. x = 16 i = 5

B. x = 16 i = 4

C. x = 8 i = 5

D. x = 32 i = 32

E. none of the above

To execute the for-loop.

  1. Execute initialization.
  2. If loop condition false,

terminate execution.

  1. Execute repetend.
  2. Execute increment,

repeat from step 2.

10

Note on ranges.

2 .. 5 contains 2, 3, 4, 5. It contains 5 +1 – 2 = 4 values

The number of values in m .. n is n +1 – m.

In the notation m..n, we require always, without saying it, that

m <= n + 1.

If m = n + 1, the range has 0 values.

2 .. 4 contains 2, 3, 4. It contains 4 +1 – 2 = 4 values

2 .. 3 contains 2, 3. It contains 3 +1 – 2 = 2 values

2 .. 2 contains 2. It contains 2 +1 – 2 = 1 values

2 .. 1 contains. It contains 1 +1 – 2 = 0 values

11

Pattern for processing range of integers:

range a..b-1 range c..d

for ( int k= a; k < b; k= k + 1) {

Process integer k;

// Print the integers in 10..n-

// inv: All ints in 10..k-1 been printed

for ( int k= 10; k < n; k= k +1) {

System.out.println(k);

}

// All ints in 10..n-1 been printed

for ( int i= c; i <= d; i= i + 1) {

Process integer i;

// Print the integers in 1..

// inv: All ints in 10..i-1 printed

for ( int i= 1; i <= 10; i= i +1) {

System.out.println(i);

}

// All ints in 10..i-1 printed

12

The pattern for processing range of integers:

range a..b-1 range c..d

for ( int i= a; i < b; i= i + 1) {

Process integer i;

// Print indices of all ‘e’s in String s

// inv: Indices of ‘e’s in s[0..s.i-1]

for ( int i= 0; i < s.length(); i= i +1) {

if (s.charAt(i) == ‘e’) 

System.out.println(i);

}

// Indices of ‘e’s in s[0..s.length()-1]

// printed

for ( int i= c; i <= d; i= i + 1) {

Process integer i;

// Store in double var. v the sum

// 1/1 + 1/2 + …+ 1/n

v= 0;

// inv: 1/1 + 1/2 + …+ 1/(i-1)

for ( int i= 1; i <= n; i= i +1) {

v= v + 1.0 / i;

}

// v= 1/1 + 1/2 + …+ 1/n

19

Development of a loop to process a range a..b-

// inv: c = no. of chars of s[0..i-1] that are in ‘0’..’9’

for ( int i= 0; i < s.length(); i= i + 1 ) {

Process integer i;

// c = no. of chars of s[0..s.length()-1] that are in ‘0’..’9’

// Set c to number of chars is String s that are digits ‘0’..’9’

How should c be initialized c?

A. c= 1; C. c= 5;

B. c= 0; D. c= -1;

20

Try these problems. Develop them using the methodology

given on slide 9. Then type them into DrJava and test them!

  1. Set c to the number of chars is String s that are digits (in 0..9).
  2. Store in res a copy of String s but with no blanks.
  3. Store in res a copy of String s but with adjacent duplicates

removed.

  1. Set boolean v to the value of “no integer in 2..n–1 divides x”.
  2. Set boolean v to the value of “every element in Vector v is an

object of class JFrame”.

  1. Add up the squares of the odd integers in the range m..n.