SFWR ENG/COMP SCI 2S03 Principles of Programming SOLUTIONS

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1 SFWR ENG/COMP SCI 2S03 Principles of Programming SOLUTIONS Day Class Midterm Exam Dr. R. Khedri DURATION : 50 minutes McMaster University Midterm Exam (CAS) October 29, 2012 Please CLEARLY print: NAME: Student ID: question mark out of total This examination paper includes 12 pages and 17 questions. You are responsible for ensuring that your copy of the paper is complete. Bring any discrepancy to the attention of your invigilator. Special Instructions : 1. The multiple-choice questions of this test must be answered on the McMaster standard OMR answer sheet (bubble form). The forms will be evaluated using McMaster optical scanner (OMR). The OMR instructions are on the next page. 2. The written questions must be answered in the space provided in this questionnaire. 3. Documents to be returned: this questionnaire, the OMR answer sheet, and all scrap paper if used. All of these documents must bear your name and student number. Only the face page of the questionnaire need to bear your name and student number, and all the loose pages of the questionnaire, if any. 4. No memory aids or textbooks of any kind are allowed during the test. No calculators, pocket computers, or PDA s are to be utilized. 5. No unauthorized scrap paper, crib sheets etc. are allowed to be used. The invigilator(s) will supply you with needed scrap paper when you ask. 6. You are not allowed to be involved in any communication of any kind concerning the questions and answers of this test with anybody except the invigilator(s) or the instructor. Any attempt of such communication will be considered a case of academic dishonesty. 7. The burden of communication is upon you. Solutions not properly explained will not be considered correct. Part of proper communication is the appearance and layout. If we cannot decode what you wrote, we cannot grade it as a correct answer. 1

2 SFWR ENG/COMP SCI 2S03 SOLUTIONS 2/12 OMR EXAMINATION - STUDENT INSTRUCTIONS NOTE: IT IS YOUR RESPONSIBILITY TO ENSURE THAT THE ANSWER SHEET IS PROPERLY COMPLETED: YOUR EXAMINATION RESULT DEPENDS UPON PROPER ATTENTION TO THESE INSTRUCTIONS. The scanner, which reads the sheets, senses the shaded areas by their non-reflection of light. A heavy mark must be made, completely filling the circular bubble, with an HB pencil. Marks made with a pen or felt-tip marker will NOT be sensed. Erasures must be thorough or the scanner may still sense a mark. Do NOT use correction fluid on the sheets. Do NOT put any unnecessary marks or writing on the sheets. 1. Print your name, student number, course name, section number and the date in the space provided at the top of Side 1 (red side) of the form. Then the sheet MUST be signed in the space marked SIGNATURE. 2. Mark your student number in the space provided on the sheet on Side 1 and fill in the corresponding bubbles underneath. 3. Mark only ONE choice from the alternatives (1,2,3,4,5, or A,B,C,D,E) provided for each question. If there is a True/False question, enter response 1 (or A) as True, and 2 (or B) as False. The question number is to the left of the bubbles. Make sure that the number of the question on the scan sheet is the same as the question number on the examination paper. 4. Pay particular attention to the Marking Directions on the form. 5. Begin answering questions using the first set of bubbles, marked "1". A picture of the answer sheet continued on page 3

3 SFWR ENG/COMP SCI 2S03 SOLUTIONS 3/12 In all the questions, we are considering Java programming language. Question 1 [1 mark] Given two boolean variables a and b, which one among the following is equivalent to the following expression?! (a && b) 1.! a &&! b 2.! a == b 3! a! b 4.! a ==! b Question 2 [1 mark] Which one of the following identifiers is valid? 1. /*a 2 salesprofit 3. int 4. double-points Question 3 [1 mark] How do we compare the value of two String objects in Java? 1. using the = operator 2. using the == operator 3 using the equals method 4. using the operator Question 4 [1 mark] What is the keyword used to instantiate an object in Java? 1. make 2. construct 3. instantiate(object) 4 new continued on page 4

4 SFWR ENG/COMP SCI 2S03 SOLUTIONS 4/12 Question 5 [1 mark] 1 p u b l i c c l a s s QuestionOne { p u b l i c s t a t i c void main ( S t r i n g [ ] args ) { 3 double length = 2. 0 ; double breadth = 4. 2 ; 5 double area = l e n g t h ( i n t ) breadth ; System. out. p r i n t f ( A r e c t a n g l e o f length %.2 f cm and breadth %.2 f cm + has area %.2 f sq. cm.%n, length, breadth, area ) ; 7 Which one among the following is the output of the above program? 1. A rectangle of length 2.00 cm and breadth 4.20 cm has area 8.40 sq. cm. 2. A rectangle of length cm and breadth cm has area sq. cm. 3. A rectangle of length 2 cm and breadth cm has area sq. cm. 4 A rectangle of length 2.00 cm and breadth 4.20 cm has area 8.00 sq. cm. Question 6 [1 mark] Which one of the following is NOT an existing wrapper class? 1. Integer 2 Char 3. Boolean 4. Double 5. Byte Question 7 [1 mark] interface (API): In a class called Test, a method foo has the following application programming public static void foo(); How would you call that method? 1 Test.foo(); 2. Test.foo(void); 3. foo.test(); 4. foo(test(void)); continued on page 5

5 SFWR ENG/COMP SCI 2S03 SOLUTIONS 5/12 Question 8 [1 mark] interface (API): In a class called Test, a method foo has the following application programming public double foo(int i, String s, char c); What is the return type of the method foo? 1 double 2. int 3. char 4. String Question 9 [1 mark] p u b l i c c l a s s QuestionTwo { 2 p u b l i c s t a t i c void main ( S t r i n g [ ] args ) { i n t a = 3 2 ; 4 i f ( a = 31) { System. out. p r i n t l n ( The value o f a i s 31 ) ; 6 e l s e { System. out. p r i n t l n ( The value o f a i s not 31 ) ; 8 10 At compile time, you get the following error: found : int required: boolean if (a = 31) { ^ 1 error Among the following, indicate the action that fixes the problem. 1. We chance the type of a to be boolean. 2. We change int a = 32; that is on Line 3 of the program to int a = boolean 32;. 3. We remove the curly brackets before and after the keyword else. 4. We change int a = 32; that is on Line 3 of the program to int a = = 32;. 5 None of the above continued on page 6

6 SFWR ENG/COMP SCI 2S03 SOLUTIONS 6/12 Question 10 [1 mark] If you want to execute a loop body at least once, what type of loop is the most appropriate than the others? 1. for loop 2. while loop 3. while loop with a counter starting with the value 1 4 do-while loop Question 11 [1 mark] statements? How many objects of the class CD exist after the execution of the following CD cd1 = new CD(); CD cd2 = cd1; 1. Two objects 2. Three objects 3. A very large number of objects 4. Zero objects 5 None of the above Question 12 [1 mark] What will the following statement print? System.out.println( ); None of the above continued on page 7

7 SFWR ENG/COMP SCI 2S03 SOLUTIONS 7/12 Question 13 [1 mark] Given the following declarations, which statement will not compile? int ival; double dval; Integer iref; Double dref; 1. iref = 12; 2. ival = iref; 3. dval = iref; 4 dref = 12; Question 14 [1 mark] p u b l i c c l a s s QuestionThree { 2 p u b l i c s t a t i c void main ( S t r i n g [ ] args ) { i n t i ; 4 double j = ; i = ( i n t ) ( j / 6) ; 6 i n t sum = 0 ; 8 while ( ( i % 10)!= 0) { sum += i ; 10 i ++; System. out. p r i n t f ( The value o f i i s %d and the value o f sum i s %d%n, i, sum) ; Which one of the following is the correct output of the above program? 1. The value of i is 10 and the value of sum is The value of i is 11 and the value of sum is 40 3 The value of i is 10 and the value of sum is The value of i is and the value of sum is continued on page 8

8 SFWR ENG/COMP SCI 2S03 SOLUTIONS 8/12 Question 15 [1 mark] 1 import java. u t i l. Scanner ; p u b l i c c l a s s QuestionSix { Consider the following program QuestionSix.java. 3 p u b l i c s t a t i c void main ( S t r i n g [ ] args ) { Scanner keyboard = new Scanner ( System. i n ) ; 5 System. out. p r i n t ( Enter the month number : ) ; i n t month = keyboard. nextint ( ) ; 7 S t r i n g monthstring ; switch ( month ) { 9 case 1 : monthstring = January ; break ; 11 case 2 : monthstring = February ; break ; 13 case 3 : monthstring = March ; break ; 15 case 4 : monthstring = April ; break ; 17 case 5 : monthstring = May ; break ; 19 d e f a u l t : a s s e r t ( month > 6) : The a s s e r t i o n i s t r i g g e r e d ; monthstring = We only handle months u n t i l 6 ; 21 break ; 23 System. out. p r i n t l n ( monthstring ) ; 25 Which one among the following is the most appropriate assessment of the above program: 1. The program does not compile due to a problem with the assertion. 2. When executed using the command java -ea QuestionSix, the program terminates without any problem for any entered integer value. 3 When executed using the command java -ea QuestionSix, the program terminates with an error message and that for some values of the variable month. 4. The program never terminates without run-time error. continued on page 9

9 SFWR ENG/COMP SCI 2S03 SOLUTIONS 9/12 Answer the two following questions in the allocated space within the corresponding program code Question 16 [3 marks] Fill in the needed code such that the program takes integer values as input from the user and finds the sum of those integers until the user types in the value -1 (which is not added). import java.util.scanner; public class QuestionFour { public static void main(string[] args) { Scanner keyboard = new Scanner(System.in); System.out.print("Enter an integer value, " + "enter -1 to stop: "); int value = keyboard.nextint(); // YOUR CODE GOES BELOW in the allocated space ANSWER: continued on page 10

10 SFWR ENG/COMP SCI 2S03 SOLUTIONS 10/12 1 import java. u t i l. Scanner ; p u b l i c c l a s s QuestionFour { 3 p u b l i c s t a t i c void main ( S t r i n g [ ] args ) { Scanner keyboard = new Scanner ( System. in ) ; 5 System. out. p r i n t ( Enter an i n t e g e r value, + e n t e r 1 to stop : ) ; i n t value = keyboard. nextint ( ) ; 7 // YOUR CODE GOES BELOW i n t sum = 0 ; 9 while ( value!= 1) { 11 sum += value ; System. out. p r i n t ( Enter an i n t e g e r value, + e n t e r 1 to stop : ) ; 13 value = keyboard. nextint ( ) ; System. out. p r i n t f ( The value o f value i s %d and the value o f sum i s %d %n, value, sum) ; continued on page 11

11 SFWR ENG/COMP SCI 2S03 SOLUTIONS 11/12 Question 17 [4 marks] Fill in the needed code such that the program prompts a user for a password. If it matches either admin or guest, then the corresponding verification success message is displayed. If it does not match, then a fail message is displayed. The user is given 3 attempts to try. If all 3 attempts fail then an all-fail message is displayed. import java.util.scanner; class PasswordVerifier { static final String ADMIN_PASSWORD = "admin"; static final String GUEST_PASSWORD = "guest"; static final int NUM_OF_ATTEMPTS = 3; public static void main(string args[]) { int attempts = NUM_OF_ATTEMPTS; String userpassword; Boolean passed = false; // If verification has succeeded. Scanner keyboard = new Scanner(System.in); // Input scanner. // Print welcome message. System.out.println("Welcome to The Password Verifier"); // Prompt user for password repeatedly until verified or out of attempts. // YOUR CODE GOES BELOW in the allocated space // Check if all attempts failed if (!passed) { System.out.println("All verification attempts failed!"); ANSWER: continued on page 12

12 SFWR ENG/COMP SCI 2S03 SOLUTIONS 12/12 / 2 =========================================================================== This Java program prompts a user f o r a password. I f i t matches e i t h e r 4 ADMIN PASSWORD or GUEST PASSWORD, then the corresponding v e r i f i c a t i o n succ es s message i s displayed. I f i t does not match, then a f a i l message i s 6 displayed. The user i s given 3 attempts to try. I f a l l 3 attempts f a i l then an a l l f a i l message i s d i s p l a y e d. 8 Written by : Tian Zhang October, =========================================================================== / import java. u t i l. Scanner ; c l a s s P a s s w o r d V e r i f i e r { s t a t i c f i n a l S t r i n g ADMIN PASSWORD = admin ; 18 s t a t i c f i n a l S t r i n g GUEST PASSWORD = guest ; s t a t i c f i n a l i n t NUM OF ATTEMPTS = 3 ; p u b l i c s t a t i c void main ( S t r i n g args [ ] ) { i n t attempts = NUM OF ATTEMPTS; 24 S t r i n g userpassword ; Boolean passed = f a l s e ; // I f v e r i f i c a t i o n has succeeded. 26 Scanner keyboard = new Scanner ( System. in ) ; // Input scanner. 28 // Print welcome message. 30 System. out. p r i n t l n ( Welcome to The Password V e r i f i e r ) ; System. out. p r i n t l n ( ) ; // Prompt user f o r password r e p e a t e d l y u n t i l v e r i f i e d or out o f attempts. while (! passed && attempts > 0) { System. out. print ( Please Enter the password ( + 38 attempts + attempt ( s ) l e f t ) : ) ; userpassword = keyboard. next ( ) ; 40 i f ( userpassword. equals (ADMIN PASSWORD) ) { 42 System. out. p r i n t l n ( V e r i f i e d as a d m i n i s t r a t o r! ) ; passed = true ; 44 e l s e { i f ( userpassword. equals (GUEST PASSWORD) ) { 46 System. out. p r i n t l n ( V e r i f i e d as guest! ) ; passed = true ; 48 e l s e { System. out. p r i n t l n ( V e r i f i c a t i o n f a i l e d! ) ; 50 attempts = attempts 1 ; // Check i f a l l attempts f a i l e d 58 i f (! passed ) { 60 System. out. p r i n t l n ( All v e r i f i c a t i o n attempts f a i l e d! ) ; THE END.