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Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

Dec 17, 2015

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Page 1: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

Nested for loops

Cont’d

Page 2: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

2

Drawing complex figures• Use nested for loops to produce the following output.

• Why draw ASCII art?– Real graphics require a lot of finesse

– ASCII art has complex patterns

– Can focus on the algorithms

#================#| <><> || <>....<> || <>........<> ||<>............<>||<>............<>|| <>........<> || <>....<> || <><> |#================#

Page 3: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

3

Development strategy• Recommendations for managing complexity:

1. Design the program (think about steps or methods needed).

• write an English description of steps required

• use this description to decide the methods

2. Create a table of patterns of characters

• use table to write your for loops

#================#| <><> || <>....<> || <>........<> ||<>............<>||<>............<>|| <>........<> || <>....<> || <><> |#================#

Page 4: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

4

1. Pseudo-code• pseudo-code: An English description of an algorithm.

• Example: Drawing a 12 wide by 7 tall box of stars

print 12 stars.for (each of 5 lines) { print a star. print 10 spaces. print a star.}print 12 stars.

************* ** ** ** ** *************

Page 5: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

5

Pseudo-code algorithm1. Line

• # , 16 =, #

2. Top half• |• spaces (decreasing)• <>• dots (increasing)• <>• spaces (same as above)• |

3. Bottom half (top half upside-down)

4. Line• # , 16 =, #

#================#| <><> || <>....<> || <>........<> ||<>............<>||<>............<>|| <>........<> || <>....<> || <><> |#================#

Page 6: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

6

Methods from pseudocode

public class Mirror { public static void main(String[] args) { drawLine(); drawTopHalf(); drawBottomHalf(); drawLine(); }

public static void drawTopHalf() { System.out.println ("drawing top"); for (int line = 1; line <= 4; line++) { // contents of each line } }

public static void drawBottomHalf() { System.out.println ("drawing bottom"); for (int line = 1; line <= 4; line++) { // contents of each line } } public static void drawLine() { // ... }}

Page 7: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

7

2. Tables• A table for the top half:

– Compute spaces and dots expressions from line number

line spaces dots

1 6 0

2 4 4

3 2 8

4 0 12

line spaces ? dots ?

1 6 6 0 0

2 4 4 4 4

3 2 2 8 8

4 0 0 12 12

#================#| <><> || <>....<> || <>........<> ||<>............<>||<>............<>|| <>........<> || <>....<> || <><> |#================#

Page 8: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

8

3. Writing the code• Useful questions about the top half:

– What methods? (think structure and redundancy)

– Number of (nested) loops per line?#================#| <><> || <>....<> || <>........<> ||<>............<>||<>............<>|| <>........<> || <>....<> || <><> |#================#

Page 9: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

9

Partial solution// Prints the expanding pattern of <> for the top half of the figure.public static void drawTopHalf() { for (int line = 1; line <= 4; line++) { System.out.print("|");

for (int space = 1; space <= (line * -2 + 8); space++) { System.out.print(" "); }

System.out.print("<>");

for (int dot = 1; dot <= (line * 4 - 4); dot++) { System.out.print("."); }

System.out.print("<>");

for (int space = 1; space <= (line * -2 + 8); space++) { System.out.print(" "); }

System.out.println("|"); }}

Page 10: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

10

Class constantsand scope

Page 11: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

11

Scaling the mirror• Modify Mirror program so it can scale.

– Mirror (left) is at size 4; right is at size 3

• Structure code so we can change the size in one place

#================#| <><> || <>....<> || <>........<> ||<>............<>||<>............<>|| <>........<> || <>....<> || <><> |#================#

#============#| <><> || <>....<> ||<>........<>||<>........<>|| <>....<> || <><> |#============#

Page 12: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

12

Limitations of variables• Idea: Make a variable to represent the size.

• Problem: A variable in one method can't be seen in others.public static void main(String[] args) { int size = 4; drawTopHalf(); drawBottomHalf();}

public static void drawTopHalf() { for (int i = 1; i <= size; i++) { // ERROR: size not found ... }}

public static void drawBottomHalf() { for (int i = size; i >= 1; i--) { // ERROR: size not found ... }}

Page 13: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

13

Scope• scope: the part of a program where a variable exists.

– From its declaration to the end of the { } braces• A variable declared in a for loop exists only in that loop.

• A variable declared in a method exists only in that method.

public static void example() { int x = 3; for (int i = 1; i <= 10; i++) { System.out.println(x); } // i no longer exists here} // x ceases to exist here

x's scopei's s

cope

Page 14: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

14

Scope implications• Variables without overlapping scope can have same

name.for (int i = 1; i <= 100; i++) { System.out.print("/");}for (int i = 1; i <= 100; i++) { // OK System.out.print("\\");}int i = 5; // OK: outside of loop's scope

• A variable can't be declared twice or used out of its scope.for (int i = 1; i <= 100 * line; i++) { int i = 2; // ERROR: overlapping scope System.out.print("/");}i = 4; // ERROR: outside scope

Page 15: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

15

Class constants• class constant: A fixed value visible to the whole

program.– value can be set only at declaration; cannot be

reassigned– declared outside of any method

• Syntax:public static final type name = value;

– name is usually in ALL_UPPER_CASE

– Examples:public static final int DAYS_IN_WEEK = 7;public static final double INTEREST_RATE = 3.5;public static final int SSN = 658234569;

Page 16: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

16

Constants and figures• Consider task of drawing the following scalable figure

(“Sign”)

+/\/\/\/\/\/\/\/\/\/\+| || || | Multiples of 5 occur many times| || |+/\/\/\/\/\/\/\/\/\/\+

+/\/\/\/\+| || | The same figure at size 2+/\/\/\/\+

Page 17: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

17

Repetitive figure codepublic class Sign {

public static void main(String[] args) { drawLine(); drawBody(); drawLine(); } public static void drawLine() { System.out.print("+"); for (int i = 1; i <= 10; i++) { System.out.print("/\\"); } System.out.println("+"); } public static void drawBody() { for (int line = 1; line <= 5; line++) { System.out.print("|"); for (int spaces = 1; spaces <= 20; spaces++) { System.out.print(" "); } System.out.println("|"); } }}

Page 18: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

18

Adding a constantpublic class Sign { public static final int HEIGHT = 5;

public static void main(String[] args) { drawLine(); drawBody(); drawLine(); } public static void drawLine() { System.out.print("+"); for (int i = 1; i <= HEIGHT * 2; i++) { System.out.print("/\\"); } System.out.println("+"); } public static void drawBody() { for (int line = 1; line <= HEIGHT; line++) { System.out.print("|"); for (int spaces = 1; spaces <= HEIGHT * 4; spaces++) { System.out.print(" "); } System.out.println("|"); } }}

Page 19: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

19

Complex figure w/ constant

• Modify the Mirror code to be resizable using a constant.

A mirror of size 4:#================#| <><> || <>....<> || <>........<> ||<>............<>||<>............<>|| <>........<> || <>....<> || <><> |#================#

A mirror of size 3:#============#| <><> || <>....<> ||<>........<>||<>........<>|| <>....<> || <><> |#============#

Page 20: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

20

Using a constant• Constant allows many methods to refer to same value:

public static final int SIZE = 4;

public static void main(String[] args) { drawTopHalf(); drawBottomHalf();}

public static void drawTopHalf() { for (int i = 1; i <= SIZE; i++) { // OK ... }}

public static void drawBottomHalf() { for (int i = SIZE; i >= 1; i--) { // OK ... }}

Page 21: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

21

Loop tables and constant• Let's modify our loop table to use SIZE

– This can change the amount added in the loop expression

#================# #============#| <><> | | <><> || <>....<> | | <>....<> || <>........<> | |<>........<>||<>............<>| |<>........<>||<>............<>| | <>....<> || <>........<> | | <><> || <>....<> | #============#| <><> |#================#

SIZE line spaces -2*line + (2*SIZE) dots 4*line - 4

4 1,2,3,4 6,4,2,0 -2*line + 8 0,4,8,12 4*line - 4

3 1,2,3 4,2,0 -2*line + 6 0,4,8 4*line - 4

SIZE line spaces dots

4 1,2,3,4 6,4,2,0 0,4,8,12

3 1,2,3 4,2,0 0,4,8

SIZE line spaces dots

4 1,2,3,4 6,4,2,0 -2*line + 8 0,4,8,12 4*line - 4

3 1,2,3 4,2,0 -2*line + 6 0,4,8 4*line - 4

Page 22: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

22

Partial solutionpublic static final int SIZE = 4;

// Prints the expanding pattern of <> for the top half of the figure.public static void drawTopHalf() { for (int line = 1; line <= SIZE; line++) { System.out.print("|");

for (int space = 1; space <= (line * -2 + (2*SIZE)); space++) { System.out.print(" "); }

System.out.print("<>");

for (int dot = 1; dot <= (line * 4 - 4); dot++) { System.out.print("."); }

System.out.print("<>");

for (int space = 1; space <= (line * -2 + (2*SIZE)); space++) { System.out.print(" "); }

System.out.println("|"); }}

Page 23: Nested for loops Cont’d. 2 Drawing complex figures Use nested for loops to produce the following output. Why draw ASCII art? –Real graphics require a.

23

Observations about constant

• The constant can change the "intercept" in an expression.– Usually the "slope" is unchanged.

public static final int SIZE = 4;

for (int space = 1; space <= (line * -2 + (2 * SIZE)); space++) { System.out.print(" ");}

• It doesn't replace every occurrence of the original value.

for (int dot = 1; dot <= (line * 4 - 4); dot++) { System.out.print(".");}


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