Control Flow Practice Problems Mr. Fahrenbacher AP Computer Science A

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1 Control Flow Practice Problems Mr. Fahrenbacher AP Computer Science A This problem set has four sections. After each section is the answer key. This problem set is NOT exhaustive, but it is too long. Find interesting questions that you want to practice and work on those. Questions Section I if/else 1. Translate each of the following English statements into logical tests that could be used in an if/else statement. Write the appropriate if statement with your logical test. Assume that three int variables, x, y,and z,have been declared. a. z is odd. b. z is not greater than y s square root. c. y is positive. d. Either x or y is even, and the other is odd. e. y is a multiple of z. f. z is not zero. g. y is greater in magnitude than z. h. x and z are of opposite signs. i. y is a nonnegative one-digit number. j. z is nonnegative. k. x is even. l. x is closer in value to y than z is. 2. Given the variable declarations int x = 4; int y = 3; int z = 4; what are the results of the following relational expressions? a. x == 4 b. x == y c. x == z d. y == z e. x + y > 0 f. x z!= 0 g. y * y <= z h. y / y == 1 i. x * (y + 2) > y - (y + z) * 2 3. Consider the following method:

2 3. Consider the following method: public static void ifelsemystery1(int x, int y) { int z = 4; if (z <= x) { z = x + 1; else { z = z + 9; if (z <= y) { y++; System.out.println(z + " " + y); What output is produced for each of the following calls? a. ifelsemystery1(3, 20); b. ifelsemystery1(4, 5); c. ifelsemystery1(5, 5); d. ifelsemystery1(6, 10); 4. Consider the following method: public static void ifelsemystery2(int a, int b) { if (a * 2 < b) { a = a * 3; else if (a > b) { b = b + 3; if (b < a) { b++; else { a ; System.out.println(a + " " + b); 5. What output is produced for each of the following calls? a. ifelsemystery2(10, 2); b. ifelsemystery2(3, 8); c. ifelsemystery2(4, 4); d. ifelsemystery2(10, 30);

3 5. Write Java code to read an integer from the user, then print even if that number is an even number or odd otherwise. You may assume that the user types a valid integer. 6. The following code contains a logic error: 7. Scanner console = new Scanner(System.in); System.out.print("Type a number: "); int number = console.nextint(); if (number % 2 == 0) { if (number % 3 == 0) { System.out.println("Divisible by 6."); else { System.out.println("Odd."); Examine the code and describe a case in which the code would print something that is untrue about the number that was entered. Explain why. Then correct the logic error in the code. 8. The following code is poorly structured: int sum = 1000; Scanner console = new Scanner(System.in); System.out.print("Is your money multiplied 1 or 2 times? "); 9. int times = console.nextint(); if (times == 1) { System.out.print("And how much are you contributing? "); int donation = console.nextint(); sum = sum + donation; count1++; total = total + donation; if (times == 2) { System.out.print("And how much are you contributing? "); int donation = console.nextint(); sum = sum + 2 * donation; count2++; total = total + donation; Rewrite it so that it has a better structure and avoids redundancy. To simplify things, you may assume that the user always types 1 or 2. (How would the code need to be modified to handle any number that the user might type?)

4 9. The following code is poorly structured: 10. Scanner console = new Scanner(System.in); System.out.print("How much will John be spending? "); double amount = console.nextdouble(); System.out.println(); int numbills1 = (int) (amount / 20.0); if (numbills1 * 20.0 < amount) { numbills1++; System.out.print("How much will Jane be spending? "); amount = console.nextdouble(); System.out.println(); int numbills2 = (int) (amount / 20.0); if (numbills2 * 20.0 < amount) { numbills2++; System.out.println("John needs " + numbills1 + " bills"); System.out.println("Jane needs " + numbills2 + " bills"); Rewrite it so that it has a better structure and avoids redundancy. You may wish to introduce a method to help capture redundant code. 12. What is wrong with the following code, which attempts to add all numbers from 1 to a given maximum? Describe how to fix the code. public static int sumto(int n) { for (int i = 1; i <= n; i++) { int sum = 0; sum += i; return sum; 13. What is wrong with the following code, which attempts to return the number of factors of a given integer n? Describe how to fix the code. public static int countfactors(int n) { for (int i = 1; i <= n; i++) { if (n % i == 0) { // factor return i;

5 14. Write code to produce a cumulative product by multiplying together many numbers that are read from the console. 15. The following expression should equal 6.8,but in Java it does not. Why not? The following code was intended to print a message, but it actually produces no output. Describe how to fix the code to print the expected message. double gpa = 3.2; if (gpa * 3 == 9.6) { System.out.println("You earned enough credits."); 22. Consider a method printtriangletype that accepts three integer arguments representing the lengths of the sides of a triangle and prints the type of triangle that these sides form. The three types are equilateral, isosceles, and scalene. An equilateral triangle has three sides of the same length, an isosceles triangle has two sides that are the same length, and a scalene triangle has three sides of different lengths. However, certain integer values (or combinations of values) would be illegal and could not represent the sides of an actual triangle. What are these values? How would you describe the precondition(s) of the printtriangletype method? 23. Consider a method getgrade that accepts an integer representing a student s grade percentage in a course and returns that student s numerical course grade. The grade can be between 0.0 (failing) and 4.0 (perfect). What are the preconditions of such a method? 24. The following method attempts to return the median (middle) of three integer values, but it contains logic errors. In what cases does the method return an incorrect result? How can the code be fixed? public static int medianof3(int n1, int n2, int n3) { if (n1 < n2) { if (n2 < n3) { else { else { return n2; return n3; if (n1 < n3) { else { return n1; return n3; 2

6 26. Consider the following Java method, which is written incorrectly: // This method should return how many of its three // arguments are odd numbers. public static void printnumodd(int n1, int n2, int n3) { int count = 0; if (n1 % 2!= 0) { count++; else if (n2 % 2!= 0) { count++; else if (n3 % 2!= 0) { count++; System.out.println(count + " of the 3 numbers are odd."); Under what cases will the method print the correct answer, and when will it print an incorrect answer? What should be changed to fix the code? Can you think of a way to write the code correctly without any if/else statements? Answers Section I 1. (a) z % 2!= 0 (b) z <= Math.sqrt(y) (c) y > 0 (d) x % 2!= y % 2 (e) y % z == 0 (f) z!= 0 (g) Math.abs(y) > Math.abs(z) (h) (x >= 0) == (z < 0) (i) y % 10 == y (j) z >= 0 (k) x % 2 == 0 (l) Math.abs(x y) < Math.abs(z y)

7 2. (a) true (b) false (c) true (d) false (e) true (f) false (g) false (h) true (i) true 3. (a) (b) 5 6 (c) 6 5 (d) (a) 10 6 (b) 9 9 (c) 3 4 (d) Scanner console = new Scanner(System.in); System.out.print("Type a number: "); int number = console.nextint(); if (number % 2 == 0) { System.out.println("even"); else { System.out.println("odd"); 6. The code incorrectly prints that even numbers not divisible by 3 are odd, because the else statement matches the most closely nested if statement (number % 3 == 0), not the outer if statement. The following change corrects the problem. Note the braces around the outer if statement: if (number % 2 == 0) { if (number % 3 == 0) { System.out.println("Divisible by 6."); else { System.out.println("Odd.");

8 8. int sum = 1000; Scanner console = new Scanner(System.in); System.out.print( "Is your money multiplied 1 or 2 times? "); int times = console.nextint(); System.out.print("And how much are you contributing? "); int donation = console.nextint(); sum += times * donation; total += donation; if (times == 1) { count1++; else if (times == 2) { count2++; If the user could type any number, the code might need additional if statements to increment the proper count variable. If the user could type anything, even a noninteger, the code might need to use the hasnextint method of the Scanner (seen in Chapter 5) to ensure that it has received valid input before it proceeds. 9. // Prompts for two people's money and reports // how many $20 bills the person would need. import java.util.*; public class Bills { public static void main(string[] args) { Scanner console = new Scanner(System.in); int numbills1 = getbills(console, "John"); int numbills2 = getbills(console, "Jane"); System.out.println("John needs " + numbills1 + " bills"); System.out.println("Jane needs " + numbills2 + " bills"); public static int getbills(scanner console, String name) { System.out.print("How much will " + name + " be spending? "); double amount = console.nextdouble(); System.out.println(); int numbills = (int) (amount/20.0); if (numbills * 20.0 < amount) { numbills++; return numbills;

9 12. The sum variable needs to be declared outside the for loop. The following code fixes the problem: public static int sumto(int n) { int sum = 0; for (int i = 1; i <= n; i++) { sum += i; return sum; 13. The method will not compile. It should count the factors using a cumulative sum; it should not return inside the loop when it finds each factor. Instead, it should declare a counter outside the loop that is incremented as each factor is seen. The following code fixes the problem: public static int countfactors(int n) { int count = 0; for (int i = 1; i <= n; i++) { if (n % i == 0) { count++; return count; 14. Scanner console = new Scanner(System.in); System.out.print("How many numbers? "); int count = console.nextint(); int product = 1; for (int i = 1; i <= count; i++) { System.out.print("Next number --> "); int num = console.nextint(); product *= num; System.out.println("Product = " + product); 15. The expression equals because the limited precision of the double type led to a roundoff error. 16. The expression gpa * 3 equals because of a roundoff error. To fix this, test that the value is close to 9.6 rather than exactly equal to it: double gpa = 3.2; if (Math.abs(gpa * 3 9.6) < 0.1) { System.out.println("You earned enough credits.");

10 22. public static void printtriangletype(int s1, int s2, int s3) { if (s1 == s2 && s2 == s3) { System.out.println("equilateral"); else if (s1 == s2 s1 == s3 s2 == s3) { System.out.println("isosceles"); else { System.out.println("scalene"); Invalid values include negative numbers for a side s length and a number for any one side length that is greater than the sum of the other two side lengths, because this cannot be a valid triangle. The precondition of the printtriangletype method is that the side lengths must constitute a valid triangle. 23. The preconditions of this method are that the grade parameter s value is between 0 and The code fails when n3 is the smallest of the three numbers; for example, when the parameters values are (4, 7, 2), the code should return 4 but instead returns 2. The method could be correctly written as follows: public static int medianof3(int n1, int n2, int n3) { if (n1 < n2 && n1 < n3) { if (n2 < n3) { return n2; else { return n3; else if (n2 < n1 && n2 < n3) { if (n1 < n3) { return n1; else { return n3; else { // (n3 < n1 && n3 < n2) if (n1 < n2) { return n1; else { return n2; Alternatively, here is a shorter version: public static int medianof3(int n1, int n2, int n3) { return Math.max(Math.max(Math.min(n1, n2), Math.min(n2, n3)), Math.min(n1, n3));

11 26. The code fails when more than one number is odd, because it uses else if rather than if. The tests should not be nested because they are not mutually exclusive; more than one number could be odd. The following code fixes the problem: public static void printnumodd(int n1, int n2, int n3) { int count = 0; if (n1 % 2!= 0) { count++; if (n2 % 2!= 0) { count++; if (n3 % 2!= 0) { count++; System.out.println(count + " of the 3 numbers are odd."); The following version without if statements also works: public static void printnumodd(int n1, int n2, int n3) { int count = n1 % 2 + n2 % 2 + n3 % 2; System.out.println(count + " of the 3 numbers are odd."); Questions Section II 14. Assume that you have a variable called count that will take on the values 1, 2, 3, 4, and so on. You are going to formulate expressions in terms of count that will yield different sequences. For example, to get the sequence 2, 4, 6, 8, 10, 12,..., you would use the expression (2 * count). Fill in the following table, indicating an expression that will generate each sequence. Sequence Expression a. 2, 4, 6, 8, 10, 12,... b. 4, 19, 34, 49, 64, 79,... c. 30, 20, 10, 0, 10, 20,... d. 7, 3, 1, 5, 9, 13,... e. 97, 94, 91, 88, 85, 82,....

12 15. Complete the code for the following for loop: for (int i = 1; i <= 6; i++) { // your code here so that it prints the following numbers, one per line: What is the output of the following oddstuff method? public static void oddstuff() { int number = 4; for (int count = 1; count <= number; count++) { System.out.println(number); number = number / 2; 17. What is the output of the following loop? int total = 25; for (int number = 1; number <= (total / 2); number++) { total = total number; System.out.println(total + " " + number); 18. What is the output of the following loop? System.out.println("+---+"); for (int i = 1; i <= 3; i++) { System.out.println("\\ /"); System.out.println("/ \\"); System.out.println("+---+"); 20. What is the output of the following loop? System.out.print("T-minus "); for (int i = 5; i >= 1; i ) { System.out.print(i + ", "); System.out.println("Blastoff!"); Answers Section II

13 14. (a) 2 * count (b) 15 * count 11 (c) 10 * count + 40 (d) 4 * count 11 (e) 3 * count for (int i = 1; i <= 6; i++) { // your code here System.out.println(18 * i 22); \ / / \ \ / / \ \ / / \ T-minus 5, 4, 3, 2, 1, Blastoff! Questions Section III 1. What output is produced by the following program? 1 public class Odds { 2 public static void main(string[] args) { 3 printodds(3); 4 printodds(17 / 2); 5 6 int x = 25; 7 printodds(37 x + 1); public static void printodds(int n) { 11 for (int i = 1; i <= n; i++) { 12 int odd = 2 * i 1; 13 System.out.print(odd + " "); System.out.println(); 16 17

14 2. What is the output of the following program? 1 public class Weird { 2 public static void main(string[] args) { 3 int number = 8; 4 halfthefun(11); 5 halfthefun( * 8); 6 halfthefun(number); 7 System.out.println("number = " + number); public static void halfthefun(int number) { 11 number = number / 2; 12 for (int count = 1; count <= number; count++) { 13 System.out.print(count + " "); System.out.println(); What is the output of the following program? 1 public class MysteryNumbers { 2 public static void main(string[] args) { 3 String one = "two"; 4 String two = "three"; 5 String three = "1"; 6 int number = 20; 7 8 sentence(one, two, 3); 9 sentence(two, three, 14); 10 sentence(three, three, number + 1); 11 sentence(three, two, 1); 12 sentence("eight", three, number / 2); public static void sentence(string three, String one, int number) { 16 System.out.println(one + " times " + three + " = " + (number * 2)); 17 18

15 4. What output is produced by the following program? 1 public class MysteryWho { 2 public static void main(string[] args) { 3 String whom = "her"; 4 String who = "him"; 5 String it = "who"; 6 String he = "it"; 7 String she = "whom"; 8 9 sentence(he, she, it); 10 sentence(she, he, who); 11 sentence(who, she, who); 12 sentence(it, "stu", "boo"); 13 sentence(it, whom, who); public static void sentence(string she, String who, String whom) { 17 System.out.println(who + " and " + whom + " like " + she); What output is produced by the following program? 1 public class MysteryTouch { 2 public static void main(string[] args) { 3 String head = "shoulders"; 4 String knees = "toes"; 5 String elbow = "head"; 6 String eye = "eyes and ears"; 7 String ear = "eye"; 8 9 touch(ear, elbow); 10 touch(elbow, ear); 11 touch(head, "elbow"); 12 touch(eye, eye); 13 touch(knees, "Toes"); 14 touch(head, "knees " + knees); public static void touch(string elbow, String ear) { 18 System.out.println("touch your " + elbow + " to your " + ear); 19 20

16 6. What output is produced by the following program? 1 public class MysterySoda { 2 public static void main(string[] args) { 3 String soda = "coke"; 4 String pop = "pepsi"; 5 String coke = "pop"; 6 String pepsi = "soda"; 7 String say = pop; 8 9 carbonated(coke, soda, pop); 10 carbonated(pop, pepsi, pepsi); 11 carbonated("pop", pop, "koolaid"); 12 carbonated(say, "say", pop); public static void carbonated(string coke, String soda, String pop) { 15 System.out.println("say " + soda + " not " + pop + " or " + coke); Write a method called printstrings that accepts a String and a number of repetitions as parameters and prints that String the given number of times with a space after each time. For example, the call printstrings("abc", 5); will print the following output: abc abc abc abc abc 9. What is wrong with the following program? 1 public class Temperature { 2 public static void main(string[] args) { 3 double tempf = 98.6; 4 double tempc = 0.0; 5 ftoc(tempf, tempc); 6 System.out.println("Body temp in C is: " + tempc); // converts Fahrenheit temperatures to Celsius 10 public static void ftoc(double tempf, double tempc) { 11 tempc = (tempf 32) * 5 / 9; 12 13

17 11. What output is produced by the following program? 1 public class MysteryReturn { 2 public static void main(string[] args) { 3 int x = 1, y = 2, z = 3; 4 z = mystery(x, z, y); 5 System.out.println(x + " " + y + " " + z); 6 x = mystery(z, z, x); 7 System.out.println(x + " " + y + " " + z); 8 y = mystery(y, y, z); 9 System.out.println(x + " " + y + " " + z); public static int mystery(int z, int x, int y) { 13 z ; 14 x = 2 * y + z; 15 y = x 1; 16 System.out.println(y + " " + z); 17 return x; Write a method called that takes three integers as parameters and returns 12. Write a method called min that takes three integers as parameters and returns the smallest of the three values; for example, a call of min(3, 2, 7) would return 2, and a call of min(19, 27, 6) would return 6. Use Math.min to write your solution. 13. Write a method called countquarters that takes an int representing a number of cents as a parameter and returns the number of quarter coins represented by that many cents. Don t count any whole dollars, because those would be dispensed as dollar bills. For example, countquarters(64) would return 2, because 64 cents is equivalent to 2 quarters with 14 cents left over. A call of countquarters(1278) would return 3, because after the 12 dollars are taken out, 3 quarters remain in the 78 cents that are left. Answer Section III number = 8

18 3. three times two = 6 1 times three = 28 1 times 1 = 42 three times 1 = 2 1 times eight = whom and who like it it and him like whom whom and him like him stu and boo like who her and him like who 5. touch your eye to your head touch your head to your eye touch your shoulders to your elbow touch your eyes and ears to your eyes and ears touch your toes to your Toes touch your shoulders to your knees toes 6. say coke not pepsi or pop say soda not soda or pepsi say pepsi not koolaid or pop say say not pepsi or pepsi 7. public static void printstrings(string s, int n) { for (int i = 1; i <= n; i++) { System.out.print(s + " "); System.out.println(); 8. is an overloaded method. 9. The program changes the value of its tempc parameter, but this doesn t affect the variable tempc in main. The (incorrect) output is: Body temp in C is: public static int min(int n1, int n2, int n3) { return Math.min(n1, Math.min(n2, n3)); 13. public static int countquarters(int cents) { return cents % 100 / 25;

19 Questions Section IV 1. For each of the following while loops, state how many times the loop will execute its body. Remember that zero, infinity, and unknown are legal answers. Also, what is the output of the code in each case? a. int x = 1; while (x < 100) { System.out.print(x + " "); x += 10; b. int max = 10; while (max < 10) { System.out.println("count down: " + max); max ; c. int x = 250; while (x % 3!= 0) { System.out.println(x); d. int x = 2; while (x < 200) { System.out.print(x + " "); x *= x; e. String word = "a"; while (word.length() < 10) { word = "b" + word + "b"; System.out.println(word); f. int x = 100; while (x > 0) { System.out.println(x / 10); x = x / 2; 2. Convert each of the following for loops into an equivalent while loop: a. for (int n = 1; n <= max; n++) { System.out.println(n); b. int total = 25; for (int number = 1; number <= (total / 2); number++) { total = total number; System.out.println(total + " " + number); d. c. int number = 4; for (int count = 1; count <= number; count++) { System.out.println(number); number = number / 2; 3. Consider the following method:

20 3. Consider the following method: public static void mystery(int x) { int y = 1; int z = 0; while (2 * y <= x) { y = y * 2; z++; System.out.println(y + " " + z); For each of the following calls, indicate the output that the preceding method produces: mystery(1); mystery(6); mystery(19); mystery(39); mystery(74); 4. Consider the following method: public static void mystery(int x) { int y = 0; while (x % 2 == 0) { y++; x = x / 2; System.out.println(x + " " + y); For each of the following calls, indicate the output that the preceding method produces: mystery(19); mystery(42); mystery(48); mystery(40); mystery(64); 10. Write a method called zerodigits that accepts an integer parameter and returns the number of digits in the number that have the value 0. For example, the call zerodigits( ) should return 2, and zerodigits(743) should return 0. The call zerodigits(0) should return 1. (We suggest you use a do/while loop in your solution.) Write a sentinel loop that repeatedly prompts the user to enter a number and, once the number 1 is typed, displays the maximum and minimum numbers that the user entered. Here is a sample dialogue: Type a number (or 1 to stop): 5 Type a number (or 1 to stop): 2 Type a number (or 1 to stop): 17 Type a number (or 1 to stop): 8 Type a number (or 1 to stop): 1 Maximum was 17 Minimum was 2 If 1 is the first number typed, no maximum or minimum should be printed. In this case, the dialogue would look like this: Type a number (or 1 to stop): 1

21 14. Consider the following variable declarations: int x = 27; int y = 1; int z = 32; boolean b = false; What is the value of each of the following Boolean expressions? a.!b b. b true c. (x > y) && (y > z) d. (x == y) (x <= z) e.!(x % 2 == 0) f. (x % 2!= 0) && b g. b &&!b h. b!b i. (x < y) == b j.!(x / 2 == 13) b (z * 3 == 96) k. (z < x) == false l.!((x > 0) && (y < 0)) 16. The following code attempts to examine a number and return whether that number is prime (i.e., has no factors other than 1 and itself). A flag named prime is used. However, the Boolean logic is not implemented correctly, so the method does not always return the correct answer. In what cases does the method report an incorrect answer? How can the code be changed so that it will always return a correct result? public static boolean isprime(int n) { boolean prime = true; for (int i = 2; i < n; i++) { if (n % i = = 0) { prime = false; else { prime = true; return prime; 19. Using Boolean Zen, write an improved version of the following method, which returns whether the given number of cents would require any pennies (as opposed to being an amount that could be made exactly using coins other than pennies): public static boolean haspennies(int cents) { boolean nickelsonly = (cents % 5 == 0); if (nickelsonly == true) { return false; else { return true;

22 20. Consider the following method: public static int mystery(int x, int y) { while (x!= 0 && y!= 0) { if (x < y) { y = x; else { x = y; return x + y; For each of the following calls, indicate the value that is returned: mystery(3, 3) mystery(5, 3) mystery(2, 6) mystery(12, 18) mystery(30, 75) 21. The following code is a slightly modified version of actual code that was in the Microsoft Zune music player in The code attempts to calculate today s date by determining how many years and days have passed since Assume the existence of methods for getting the total number of days since 1980 and for determining whether a given year is a leap year: int days = gettotaldayssince1980(); year = 1980; while (days > 365) { // subtract out years if (isleapyear(year)) { if (days > 366) { else { days = 366; year += 1; days = 365; year += 1; Thousands of Zune players locked up on January 1, 2009, the first day after the end of a leap year since the Zune was released. (Microsoft quickly released a patch to fix the problem.) What is the problem with the preceding code, and in what cases will it exhibit incorrect behavior? How can it be fixed? 22. Consider the following variable declarations: int x = 27; int y = 1; int z = 32; boolean b = false; Write a new Boolean expression that is the negation of each of the following Boolean expressions. Use De Morgan s laws rather than simply writing a! at the beginning of each entire expression. a. b b. (x > y) && (y > z) c. (x == y) (x <= z)

23 d. (x % 2!= 0) && b e. (x / 2 == 13) b (z * 3 == 96) f. (z < x) && (z > y x >= y) Section 5.4: User Errors Answers Section IV 1. (a) Executes body 10 times. Output is (b) Executes body 0 times. No output. (c) Loops infinitely. Output is (d) Executes body 3 times. Output is (e) Executes body 5 times. Output is bbbbbabbbbb (f) Executes body 7 times. Output is (a) int n = 1; while (n <= max) { System.out.println(n); n++; (b) int total = 25; int number = 1; while (number <= (total / 2)) { total = total number; System.out.println(total + " " + number); number++; (c) int i = 1;

24 (d) int number = 4; int count = 1; while (count <= number) { System.out.println(number); number = number / 2; count++; Method call Output mystery(1); 1 0 mystery(6); 4 2 mystery(19); 16 4 mystery(39); 32 5 mystery(74); Method call Output mystery(19); 19 0 mystery(42); 21 1 mystery(48); 3 4 mystery(40); 5 3 mystery(64); ! public static int zerodigits(int number) { if(number == 0) { return 1; int count = 0; while(number > 0) { if(number % 10 == 0) { count++; number /= 10; return count;

25 13. int SENTINEL = -1; System.out.print("Type a number (or " + SENTINEL + " to stop): "); Scanner console = new Scanner(System.in); int input = console.nextint(); int min = input; int max = input; while (input!= SENTINEL) { if (input < min) { min = input; else if (input > max) { max = input; System.out.print("Type a number (or " + SENTINEL + " to stop): "); input = console.nextint(); if (min!= SENTINEL) { System.out.println("Maximum was " + max); System.out.println("Minimum was " + min); 14. (a) true (b) true (c) false (d) true (e) true (f) false (g) false (h) true (i) true (j) true (k) true (l) false 16. In this code the boolean flag isn t being used properly, because if the code finds a factor of the number, prime will be set to false, but on the next pass through the loop, if the next number isn t a factor, prime will be reset to true again. The following code fixes the problem: public static boolean isprime(int n) { boolean prime = true; for (int i = 2; i < n; i++) { if (n % i == 0) { prime = false; return prime;

26 19. public static boolean haspennies(int cents) { return cents % 5!= 0; 20. Method call Value returned mystery(3, 3) 3 mystery(5, 3) 1 mystery(2, 6) 2 mystery(12, 18) 6 mystery(30, 75) The code will get stuck in an infinite loop when the current date is the end of a leap year. On December 31 the days value will be 366, so code enters the if (isleapyear) statement but does not enter the if (days > 366) statement. So the loop does not subtract any days and never terminates. The code can be fixed by adding a break statement to the loop (see Appendix D): int days = gettotaldayssince1980(); year = 1980; while (days > 365) { // subtract out years if (isleapyear(year)) { if (days > 366) { days -= 366; year += 1; else { // break; // new code here // else { days -= 365; year += 1; 22. (a)!b (b) (x <= y) (y <= z) (c) (x!= y) && (x > z) (d) (x % 2 == 0)!b (e) (x / 2!= 13) &&!b && (z * 3!= 96) (f) (z >= x) (z <= y && x < y) 23.