1Chapter 7 Chapter 7 --IterationIterationChapter GoalsChapter GoalsProgram Program repitiationrepitiationstatements statements ––or loops or loops ––with the with the for, while, and dofor, while, and do--while statementswhile statementsLearn potential pitfalls of infinite loops and off by one Learn potential pitfalls of infinite loops and off by one errorserrorsUnderstand nested loopsUnderstand nested loopsProcess inputProcess inputChapter 7Chapter 7Control statementsControl statementsAlready learned about selection statementsAlready learned about selection statementsNow learn about Now learn about repetition statements, repetition statements, ororloop loop statementsstatementsRepetition statementsRepetition statements––repeat a block of code repeat a block of code for a fixed number of times, or until some for a fixed number of times, or until some condition is metcondition is met3 types: 3 types: whilewhile, , dodo--whilewhile, and , and forforWhile statementWhile statementWhileWhilestatements/loops, repeat a body of code statements/loops, repeat a body of code until some condition is metuntil some condition is metThis is helpful for certain problems such as:This is helpful for certain problems 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 statementWhile statementSyntax:Syntax:while ( <while ( <booleanbooleanexpression> )expression> )<statement> <statement> //AKA //AKA loop bodyloop bodySimilar to Similar to if statementsif statements––if the <statement> block if the <statement> block is a is a singlesinglestatement, 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 as long Keeps executing the <statement> block as long as as <<booleanbooleanexpression>expression>is is truetrueExampleExampleAdd integers 1 through 100 (1+2+…+100)Add integers 1 through 100 (1+2+…+100)intintsum = 0, number = 1;sum = 0, number = 1;//Important to //Important to ////intializeintializewhile ( number <= 100 ){while ( number <= 100 ){////booleanbooleanexpressionexpressionsum = sum = sumsum+ number;+ number;number++;number++;// what does this do?// what does this do?}}2ififFlow DiagramFlow Diagramconditionbodyfalsetruewhile while Flow DiagramFlow DiagramconditionbodyfalsetrueExampleExampleintintbottlesOfBeerbottlesOfBeer= 99= 99while (while (bottlesOfBeerbottlesOfBeer> 0){> 0){System.out.println(bottlesOfBeerSystem.out.println(bottlesOfBeer+” on the wall”);+” on the wall”);System.out.println(bottlesOfBeerSystem.out.println(bottlesOfBeer+” on the wall”);+” on the wall”);bottlesOfBeerbottlesOfBeer----;;System.out.println(“TakeSystem.out.println(“Takeone down, pass it around);one down, pass it around);System.out.println(bottlesOfBeerSystem.out.println(bottlesOfBeer+” on the wall”);+” on the wall”);}}Compound BalanceCompound BalanceProblem: Want to calculate how many years my Problem: Want to calculate how many years my balance will take to appreciate to $20,000 given I balance will take to appreciate to $20,000 given I start $10,000 and have a 5% interest ratestart $10,000 and have a 5% interest rateintintyears = 0;years = 0;Scanner in = new Scanner in = new Scanner(System.inScanner(System.in););System.out.printSystem.out.print(“Enter target balance: “);(“Enter target balance: “);intinttargetBalancetargetBalance= = in.nextIntin.nextInt();();while (balance < while (balance < targetBalancetargetBalance)){{year++;year++;double interest = balance * rate / 100;double interest = balance * rate / 100;balance = balance = balancebalance+ interest;+ interest;}}System.out.println(“YourSystem.out.println(“Yourtarget will be target will be achieved in “+ years + “ years.”);achieved in “+ years + “ years.”);3while (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?Common Error 7.1Common Error 7.1Most common mistake Most common mistake ––loop is never loop is never terminatedterminated<<booleanbooleanexpression> is always trueexpression> is always trueInfinite loop Infinite loop ––have to close program (have to close program (Ctrl+cCtrl+c))intintcount = 1;count = 1;while (count != 10){while (count != 10){count += 2;count += 2;}}intintproduct = 0;product = 0;while (product < 500000){while (product < 500000){product *= 5;product *= 5;}}Infinite loopInfinite loopCommon cause Common cause ––not advancing variablenot advancing variableintintyears = 0;years = 0;while (years < 20){while (years < 20){double interest = balance * rate / 100;double interest = balance * rate / 100;balance = balance = balancebalance+ interest;+ interest;}}Common cause Common cause ––increment vs. decrementincrement vs. decrementintintyears = 20;years = 20;while (years > 0){while (years > 0){years++;years++;double interest = balance * rate / 100;double interest = balance * rate / 100;balance = balance = balancebalance+ interest;+ interest;}}OverflowOverflow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 = countcount+ .333333333333333+ .333333333333333}}UnderflowUnderflowReal numbers are not always stored exactly, Real numbers are not always stored exactly, sometimes an approximation is neededsometimes an approximation is neededdouble count = 0;double count = 0;while (count != 1.0){while (count != 1.0){count = count = countcount+ 1.0/3.0;+ 1.0/3.0;}//May not work!}//May not work!Off by oneOff by oneAnother common error is to be off by oneAnother common error is to be off by oneintintcount = 1;count = 1;while (count < 10){while (count < 10){……count++;count++;}}How many executions?How many executions?intintcount = 0;count = 0;while (count <= 10){while (count <= 10){……count++;count++;}}How many executions?How many executions?4Off by