ANSWERS. Birkbeck (University of London) Software and Programming 1 In-class Test Feb Student Name Student Number. Answer all questions

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1 Birkbeck (University of London) Software and Programming 1 In-class Test Feb 2018 Student Name Student Number Answer all questions 1. Consider the following sequence of Java statements: int i = 4; int j = 7 - i; i = 4 + i / j * 2-2; j = 32 / i - i * 2; What is the value of j after these statements are executed? Show your workings. (7 marks) 0 Workings: (a) j = 3, (b) i = / 3 * 2-2 = 4, (c) j = 32/4-4*2 = 0 COIY018H5 Page 1 of 7 c Birkbeck College 2018

2 2. Given a variable word of type String, write an expression of type boolean, which is evaluated to true if the word contains between 3 and 12 (inclusive) characters and does not end in "ed", and to false otherwise. (7 marks) word.length() >= 3 && word.length() <= 12 &&!word.substring(word.length()-2, word.length()).equals("ed") sp pdf / p. 18 and p True or false? (a) A method with return type void must print a result. (b) When executing a return statement, the method exits immediately. (c) A method has at most one return statement. (d) A method has at least one return statement. Only (b) is true. sp pdf, pp. 5 & 28 (4 marks) 4. Which of the following are valid Java identifiers (i.e., possible names of variables/methods)? (a) Int (b) for each (c) FreeForAll (d) 2b (e) STRING (f) void (g) call (a), (b), (c), (e), (g) sp pdf / p. 20 (7 marks) COIY018H5 Page 2 of 7 c Birkbeck College 2018

3 5. Identify and explain five compile-time errors in the following Java code: public class foo bar { public static int f(int NUMBER) { for (int number = 2; number =< NUMBER; number++) { boolean prime = true; for (int divisor = 2; prime && divisor < number; divisor++) if (0 == number % divisor) prime = false ; System.out.println(number + " is" + prime? " " : "n t" + " prime"); How would you correct the errors you have found (with as few changes as possible)? (10 marks) public class foo bar { public static void f(int NUMBER) { // not int for (int number = 2; number <= NUMBER; number++) { // not =< boolean prime = true; for (int divisor = 2; prime && divisor < number; divisor++) if (0 == number % divisor) prime = false; // no System.out.println(number + " is" + (prime? " " : "n t") + " prime"); // brackets (? : is of lowest precedence) // missing COIY018H5 Page 3 of 7 c Birkbeck College 2018

4 6. Implement a method getdegreeclassification to determine the degree classification given the average marks of a student. The method should take one argument of type int, the average mark, and return a String, the degree classification according to the following table: average marks Pass 0 29 Fail classification public static String getdegreeclassification(int avg) { if (avg >= 70) return "1"; if (avg >= 60) return "2.1"; if (avg >= 50) return "2.2"; if (avg >= 40) return "3"; if (avg >= 30) return "Pass"; return "Fail"; (10 marks) COIY018H5 Page 4 of 7 c Birkbeck College 2018

5 7. What is printed as a result of executing the following fragment of code? int v = 0; int a = v + 4; while (v < 40) { v = a + 6; System.out.println(v + 5); a = v + 4; Show your workings Workings: v a v < 40 new v printout v - 5 new a 0 4 true true true true false (10 marks) 8. What are the type and the value of the following expression s.substring(0,4).equals("java") && b % 2 == 1 && s.length() / (b % 2) > 2? "true" : "false" with the following declarations: String s = "javascript"; int b = 6;? String and "false" (because the second argument of the first logical AND is false) (5 marks) COIY018H5 Page 5 of 7 c Birkbeck College 2018

6 9. Implement a method that returns true if its argument of type String is a word that (a) contains a lower-case letter and (b) does not contain a hyphen (-). (20 marks) public static boolean matchword(string s) { boolean founduc = false; for (int i = 0; i < s.length(); i++) { char c = s.charat(i); if (Character.isLowerCase(c)) founduc = true; if (c == - ) return false; return founduc; COIY018H5 Page 6 of 7 c Birkbeck College 2018

7 10. (a) Transform the for loop in the following fragment of code into a while loop. String s = ""; for (int i = 0; i < a.length; i++) if (i % 2 == 1) s = s + a[i]; System.out.println("result: " + s); (b) Suppose that a is declared as follows: int[] a = { 0, 2, 1, 3, 4, 10 ;. What is printed out as a result of executing this fragment of code? (c) Explain the action of this fragment of code (for an array a of integers). (20 marks) (a) String s = ""; int i = 0; // first argument of the for loop while (i < a.length) { // second argument of the for loop turns into // the while condition if (i % 2 == 1) s = s + a[i]; i++; // do not forget the third argument of the for loop // and the curly brackets System.out.println("result: " + s); (b) The output is: result: 2310 (c) The program prints elements of the given array with odd indexes (without any spaces). COIY018H5 Page 7 of 7 c Birkbeck College 2018