Chapter 7 - IterationChapter GoalsControl StatementsWhile LoopsSlide 5Exampleif Flow Diagramwhile Flow DiagramSlide 9Compound BalanceSlide 11Slide 12Slide 13Infinite LoopsSlide 15Overflow ErrorUnderflow ErrorOff by One ErrorSlide 19do-while Statementsdo-while: Syntaxdo-while vs whileSlide 23do-while Flow DiagramSlide 25Slide 26Example: InputExample: while versionAvoid Repeat CodeSlide 30For LoopsFor Loops: Syntaxfor Flow DiagramSum ExampleSlide 35Interest ExampleSlide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43ScopeIs this legal?Nested LoopsMultiplication TablePracticeSlide 49Slide 50Counting LoopsSentinel LoopsSlide 53Loop and a halfTipsAlternatives to loop and a halfbreakCode JumpsSpaghetti CodeWhich loop to choose?Random NumbersSlide 62Slide 63Loop InvariantsChapter 7 - Chapter 7 - IterationIterationChapter GoalsChapter GoalsProgram repetiation statements – loops – Program repetiation statements – loops – with with forfor, , whilewhile, and , and do-whiledo-while statementsstatementsLearn potential pitfalls of infinite loops Learn potential pitfalls of infinite loops and off by one errorsand off by one errorsUnderstand nested loopsUnderstand nested loopsProcess inputProcess inputControl StatementsControl StatementsAlready learned about selection Already learned about selection statementsstatementsNow learn about Now learn about repetition repetition statements, statements, oror loop statements loop statementsRepetition statementsRepetition statements – repeat a – repeat a block of code for a fixed number of block of code for a fixed number of times, or until some condition is mettimes, or until some condition is met3 types: 3 types: whilewhile, , do-whiledo-while, and , and forforWhile LoopsWhile LoopsWhileWhile statements/loops, repeat a body statements/loops, repeat a body of code until some condition is metof code until some condition is metThis is helpful for certain problems This is helpful for certain problems such as:such as:Feed cat until it is fullFeed cat until it is fullDrink beer until pitcher is doneDrink beer until pitcher is doneGet user input until they hit the Esc keyGet user input until they hit the Esc keyPlay a game until someone winsPlay a game until someone winsWhile LoopsWhile LoopsSyntax:Syntax:while ( <boolean expression> )while ( <boolean expression> )<statement> <statement> //AKA //AKA loop bodyloop bodySimilar to Similar to if statementsif statements – if the – if the <statement> block is a <statement> block is a singlesingle statement, curly braces are not indeedstatement, curly braces are not indeedNormally, it is a block statementNormally, it is a block statementKeeps executing the <statement> block Keeps executing the <statement> block as long as as long as <boolean expression><boolean expression> is is truetrueExampleExampleAdd integers 1 through 100 (1+2+…Add integers 1 through 100 (1+2+…+100)+100)int sum = 0, number = 1;int sum = 0, number = 1;// Important to // Important to ////intializeintializewhile ( number <= 100 ) {while ( number <= 100 ) {//boolean expression//boolean expressionsum = sum + number;sum = sum + number;number++;number++;// what does this do?// what does this do?}}ifif Flow Diagram Flow Diagramconditionbodyfalsetruewhile while Flow DiagramFlow DiagramconditionbodyfalsetrueExampleExampleint bottlesOfBeer = 99int bottlesOfBeer = 99while (bottlesOfBeer > 0){while (bottlesOfBeer > 0){System.out.println(bottlesOfBeer+” on the wall”);System.out.println(bottlesOfBeer+” on the wall”);System.out.println(bottlesOfBeer+” on the wall”);System.out.println(bottlesOfBeer+” on the wall”);bottlesOfBeer--;bottlesOfBeer--;System.out.println(“Take one down, pass it around);System.out.println(“Take one down, pass it around);System.out.println(bottlesOfBeer+” on the wall”);System.out.println(bottlesOfBeer+” on the wall”);}}Compound BalanceCompound BalanceProblem: Want to calculate how Problem: Want to calculate how many years my balance will take to many years my balance will take to appreciate to $20,000 given I start appreciate to $20,000 given I start $10,000 and have a 5% interest rate$10,000 and have a 5% interest rateint years = 0;int years = 0;Scanner in = new Scanner(System.in);Scanner in = new Scanner(System.in);System.out.print ("Enter target balance: ");System.out.print ("Enter target balance: ");int targetBalance = in.nextInt();int targetBalance = in.nextInt();while (balance < targetBalance)while (balance < targetBalance){{year++;year++;double interest = balance * rate / 100;double interest = balance * rate / 100;balance = balance + interest;balance = balance + interest;}} System.out.println("Your target will be achieved System.out.println("Your target will be achieved in " + years + " years.");in " + years + " years.");While LoopsWhile Loopswhile (true){while (true){<statement><statement>}}How long will this loop run?How long will this loop run?Why would we want to do thisWhy would we want to do thisCan we stop it?Can we stop it?Infinite LoopsInfinite LoopsMost common mistake – loop is never Most common mistake – loop is never terminatedterminated<boolean expression> is always true<boolean expression> is always trueInfinite loop –Infinite loop – have to close program have to close program (Ctrl+c)(Ctrl+c)int count = 1;int count = 1;while (count != 10){while (count != 10){count += 2;count += 2;}}int product = 0;int product = 0;while (product < 500000){while (product < 500000){product *= 5;product *= 5;}}Infinite LoopsInfinite LoopsCommon cause – not advancing variableCommon cause – not advancing variableint years = 0;int years = 0;while (years < 20){while (years < 20){double interest = balance * rate / 100;double interest = balance * rate / 100;balance = balance + interest;balance = balance + interest;}}Common cause – increment vs. Common cause – increment vs. decrementdecrementint years = 20;int years = 20;while (years > 0){while (years > 0){years++;years++;double interest = balance * rate / 100;double interest = balance * rate / 100;balance = balance + interest;balance = balance + interest;}}Overflow ErrorOverflow ErrorValue of a variable exceeds precisionValue of a variable exceeds precisionshort s;short s;while (s < 3000){while (s < 3000){s++;s++;}}double count = 0;double count = 0;while (count != 1.0){while (count != 1.0){count = count + .333333333333333count = count