comp 110 augustus gloop, augustus gloop luv kohli september 24, 2008 mwf 2-2:50 pm sitterson 014

COMP 110COMP 110Augustus GAugustus Glooploop, Augustus G, Augustus Glooploop……

Luv KohliSeptember 24, 2008

MWF 2-2:50 pmSitterson 014

AnnouncementsAnnouncementsProgram 2 due Friday, 2pm◦Remember to also print out your code and

hand it in

I will be out of town on Friday◦Recitation will still be held by another

COMP110 instructor at the usual time◦No office hours Friday morning

Ask me questions before 6pm Thursday

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Some notes about printing your codeSome notes about printing your code

Print from jGRASP if you can

Print with a fixed-width font (such as Consolas or Courier New)

Print double-sided if you can

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Questions?Questions?

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Today in COMP 110Today in COMP 110Nested loops

Some comments on Lab 3

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Nested loopsNested loopsJust like we have nested if/else

statements, we can have nested loops

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Nested loops example: friendly greetingsNested loops example: friendly greetings

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Nested loops example: friendly greetingsNested loops example: friendly greetings

Student 1 shakes Student 4’s handStudent 1 shakes Student 5’s handStudent 1 shakes Student 6’s handStudent 2 shakes Student 4’s handStudent 2 shakes Student 5’s handStudent 2 shakes Student 6’s handStudent 3 shakes Student 4’s handStudent 3 shakes Student 5’s handStudent 3 shakes Student 6’s hand

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Nested loops example: friendly greetingsNested loops example: friendly greetings

Student 1 shakes Student 4’s hand shakes Student 5’s hand shakes Student 6’s handStudent 2 shakes Student 4’s hand shakes Student 5’s hand shakes Student 6’s handStudent 3 shakes Student 4’s hand shakes Student 5’s hand shakes Student 6’s hand

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Nested loops example: friendly greetingsNested loops example: friendly greetings

for (every student in line A){ Student in line A shakes every Student’s hand in line B}

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Nested loops example: friendly greetingsNested loops example: friendly greetings

for (every student in line A){ for (every student in line B) { (Student in line A) shakes (Student in line

B)’s hand }}

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Inner loopOuter loop

Nested loops example: friendly greetingsNested loops example: friendly greetings

for (int stdLineA = 1; stdLineA <= 3; stdLineA++){ for (int stdLineB = 4; stdLineB <= 6; stdLineB+

+) { System.out.println(“Student ” + stdLineA + “ shakes Student ” + stdLineB + “’s hand.”); }}

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stdLineA123

stdLineB456

Nested loops example: friendly greetingsNested loops example: friendly greetings

for (int stdLineA = 1; stdLineA <= 3; stdLineA++){ for (int stdLineB = 4; stdLineB <= 6; stdLineB+

+) { System.out.println(“Student ” + stdLineA + “ shakes Student ” + stdLineB + “’s hand.”); }}

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Inner loop

Outer loop

Nested loopsNested loopsYou can nest different kinds of loops

inside other loops, or put if/else statements inside loops, or put loops inside if/else statements, or…

ExamAverager example in jGRASP

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Loop bugsLoop bugsInfinite loops – already talked about

these

Off-by-one errors

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Off-by-one errorsOff-by-one errorsLoop repeats one too many or one too

few times

for (count = 1; count < 10; count++) // loop 9 times: 1, 2, 3, ... 9

for (count = 1; count <= 10; count++) // loop 10 times: 1, 2, 3, ... 10

for (count = 0; count < 10; count++) // loop 10 times: 0, 1, 2, ... 9

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Finding errorsFinding errorsTrace your variables◦ Put output statements in your code to see what

values are stored in your variables System.out.println(variable); Check whether the values are correct and what you expect

◦ Remove these extra output statements after the program runs correctly

◦ Read example in the book, p. 188 (4th edition), p. 218 (5th edition)

Use a debugger

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What does this code do?What does this code do? int a = 0; int b = 0; for (int i = 1; i <= 6; i++) { if (i % 2 == 0) { b = b + i;} else {a = a + i;}}

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What does this code do?What does this code do? int oddSum = 0; int evenSum = 0; for (int i = 1; i <= 6; i++) { if (i % 2 == 0) { evenSum = evenSum + i;} else {oddSum = oddSum + i;}}

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What does this code do?What does this code do?int oddSum = 0;int evenSum = 0;for (int i = 1; i <= 6; i++){ if (i % 2 == 0) { evenSum = evenSum + i; } else { oddSum = oddSum + i; }}

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What is wrong with this code?What is wrong with this code? int oddSum = 0; int evenSum = 0; for (int i = 1; i <= 6; i++) { if (i % 2 == 0) evenSum = evenSum + i;} else {oddSum = oddSum + i;}}

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What is wrong with this code?What is wrong with this code?int oddSum = 0;int evenSum = 0;for (int i = 1; i <= 6; i++){ if (i % 2 == 0) evenSum = evenSum + i; } else { oddSum = oddSum + i; }}

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IndentationIndentationIndentation◦Makes code easier to read◦Helps with finding syntax and logic errors◦ Indent code that goes between { and }

Be consistent!

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ScopeScopeVariables declared in outer scopes are

visible to code inside inner scopes

public static void main(String[] args) { int total = 15; int n = 5; if (n <= 10) { total = total + n; } System.out.println(total); }

outer inner

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ScopeScopeVariables declared in inner scopes are

NOT visible to outer code

public static void main(String[] args) { int n = 5; if (n <= 10) { int total = 15 + n; } System.out.println(total); // ERROR!!! }

outerinner

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elseelseif (inputString.equals(“BLUE”)) eyeColor = Color.BLUE;else if (inputString.equals(“GREEN”)) eyeColor = Color.GREEN;else if (inputString.equals(“RED”)) eyeColor = Color.RED;else if (!inputString.equals(“BLUE”) && !inputString.equals(“GREEN”) && !inputString.equals(“RED”)) eyeColor = Color.WHITE;

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elseelseif (inputString.equals(“BLUE”)) eyeColor = Color.BLUE;else if (inputString.equals(“GREEN”)) eyeColor = Color.GREEN;else if (inputString.equals(“RED”)) eyeColor = Color.RED;else eyeColor = Color.WHITE;

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elseelse not needed when empty not needed when emptyif (inputString.equals(“MOUTH”)){ mouthStartAngle = 0;}else{}

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Multi-line commentsMulti-line comments/* This is a multi-line comment. What do you think of it? */

// You can also have multi-line comments// this way.

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Too many commentsToo many commentsDon’t need to comment every line of code,

especially when it is obvious what your code is doing

// set count to 12count = 12;

Only comment to enhance understanding and to explain why your code does what it does

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FridayFridayProgram 2 due, 2pm

Lab 4 help

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