Answer the following questions on the answer sheet that is provided. The computer must be switched off while you are busy with Section A.

Transcription

1 UNIVERSITY OF THE FREE STATE DEPARTMENT OF COMPUTER SCIENCE AND INFORMATICS RIS 114 DATE: 25 April 2013 TIME: 180 minutes MARKS: 100 ASSESSORS: Prof. P.J. Blignaut & Mr. F. Radebe (+2 bonus marks) MODERATOR: Dr. L. de Wet SECTION A (45) Answer the following questions on the answer sheet that is provided. The computer must be switched off while you are busy with Section A. 1. What is a namespace? (1) 2. How do we add a namespace to a program? (1) 3. What is an algorithm? (1) 4. Evaluate the following expressions. Write down the answer only: / / % > 5 (4) 5. Provide the most suitable data type for each of the following variable declarations: 5.1 Name = John ; 5.2 Length = 3.4; 5.3 Salary; 5.4 StudentNumber; (4) 6. Provide the output of each of the following program segments: 6.1 int x = 9; Console.WriteLine((x++).ToString()); 6.2 int x = 12 % 5; Console.WriteLine((++x).ToString()); 6.3 int x = 5; x *= 3; Console.WriteLine(x.ToString()); 6.4 int i = 3; do Console.WriteLine(i); i--; while (i >= 0); Console.WriteLine(i); (6)

2 7. What is another way of writing the following expression? ans *= v1-1; 2 A. ans = v1 * ans - 1; B. ans = ans * v1--; C. ans = v1 *(ans- 1); D. ans = ans *--v1; (2) 8. How can the compound conditional expression ( (average > 79) && (average <= 89) ) be written to eliminate the logical operator, without changing the logic? A. remove the && and create a nested if statement B. (average > 79 <= 89) C. by replacing the && with D. (79 > average <= 89) (2) 9. Name and explain or give examples of three types of programming errors. (6) 10. What is meant by the term defensive programming? (1) 11. What do the terms Step into and Step over mean when referring to debugging of a program? (2) 12. Name two special types of methods. (2) 13. What are overloaded methods? (2) 14. What is the difference between a formal parameter and an actual parameter? (2) 15. What is the difference between a value parameter and a reference parameter? (2) 16. What is the meaning of void when used as the return type of a method? (1) 17. What are the advantages of methods? In other words, why do we use methods and do not put all code in one long block of code? (2) 18. What is a counter-controlled loop? (1) 19. When is it advisable to use post-test loops? (2) 20. What is the basic principle of recursion? (1) NB. You must submit Section A before you may switch on the computer to do Section B. [45]

3 3 SECTION B (57) Answer the following questions by developing the solutions in C#. Make sure that you enter your name, student number and question number for every question in a comment block at the top of the code window. You will not get marks if you do it, but you will lose 3 marks for every question if you don t do it. You might even get zero for the entire test if you don t do it! Make sure that you give appropriate names to all controls and variables. Create the following folder on the T-drive in the format Studentnumber_Surname, e.g _Blignaut Note that this is not an open-book test. Question 1 The highest common factor (HCF) of two integers m and n can be determined by dividing the bigger one by the smaller one and then replacing the bigger with the smaller and the smaller with the remainder after division. The process must be repeated until the remainder is 0. The smaller number is the HCF of the two original numbers. Develop a flowchart for this scenario. (9) Question 2 Write a program for the console window which will allow the user to enter a non-negative angle θ in degrees. The program must then display the sine of the angle. Provide the answer in the format sin(θ) = value, for example sin(45) = Ensure that the user enters a valid non-negative numeric value for the angle. An angle larger than 360 must be converted to an angle between 0 and 360. Hints: - The Math class contains a method Sin() that takes an angle in radians as parameter. - π radians = 180. (15) Question 3 Develop a console application that will generate n random integers between 0 and 1000 (both including). The user must be able to enter n, the number of random numbers to generate (no error handling necessary). Display the percentage of even numbers and the percentage of odd numbers that was generated. Hint: The Random class contains a method Next() that takes the lower and upper limits as parameters and returns a random number. Use the Help and Intellisense to get examples and determine the exact syntax and usage. (20)

4 4 Question 4 Consider the following Main method which is used to determine if a given integer is prime. Create a new Console application and copy the code from this Main method. Implement the method IsPrime. You may not alter the Main method in any way. No error handling is necessary. (13) Note: A prime number is a number that does not have any factors besides 1 and itself. static void Main(string[] args) Console.Write ("Enter number: "); int inumber = int.parse(console.readline()); if (IsPrime(iNumber)) Console.WriteLine(iNumber.ToString() + " is prime."); else Console.WriteLine(iNumber.ToString() + " is not prime."); Console.Write("Press any key to exit..."); Console.ReadKey(); //Main

5 5 ANSWER SHEET Student number: Name and surname: 1. Namespace: 2. Add namespace: 3. Algorithm: / 5.0 : / 5 : % 5 : > 5 : 5.1 Name = John ; 5.2 Length = 3.4; 5.3 Salary; 5.4 StudentNumber; Programming errors:

6 6 10. Defensive programming: 11. Step over: Step into: 12. Special types of methods: 13. Overloaded methods: 14. Formal parameter: Actual parameter: 15. Value parameter: Reference parameter: 16. void: 17. Advantages of methods: 18. Counter-controlled loop: 19. Post-test loop: 20. Recursion:

7 Section A (45) 7 MEMORANDUM 1. Namespace: Group / bundle of classes 2. Add namespace: using / precede class name 3. Algorithm: Process or logic to follow to solve a problem / 5.0 : / 5 : % 5 : > 5 : true 5.1 string Name = John ; 5.2 double Length = 3.4; 5.3 decimal Salary; 5.4 string StudentNumber; D 8. A 9. Syntax error : Error with syntax of programming language. Program does not compile, e.g. missing ; Runtime error : Program compiles but error occurs during runtime, e.g. user entering a non-numeric value when numeric input was expected. Logical error: Program compiles but provides wrong output, e.g. avg = t1 + t2 /2; 10. Defensive programming: Make provision for runtime errors. 11. Step over: Debugger calls a method that is called without going into it. Step into: Debugger goes into a method that is called. 12. Special types of methods: Constructor, event handlers 13. Overloaded methods have the same names but different signatures 14. Formal parameter in method signature / definition Actual parameter in method call 15. Value parameter: Actual and formal parameters occupy different memory cells. Value is copied from the actual parameter to the formal parameter when the method is called. Reference parameter: Actual and formal parameters refer the same memory cell. A change in the scope of either the actual or formal parameter is known in the scope of the other. 16. void: Method does not return a value 17. Advantages of methods: - Avoid repetition - Separate logic 18. Counter keeps track of the number of times that a loop is executed 19. Post-test loop: Condition must be tested after the loop The loop must be executed at least once. 20. Recursion: A method calls itself.

8 8 Question 1 Section B One mark per arrow, excluding Start & Stop (9). Question 2 Console app static void Main(string[] args) try //Input Console.Write("Angle in degrees: "); int theta = int.parse(console.readline()); if (theta < 0) Console.WriteLine("Invalid input."); else //Processing theta = theta % 360; //Convert to number in [0,360] double radians = theta * Math.PI / 180; double dsin = Math.Sin(radians); //Output Console.WriteLine("sin(" + theta + ") = " + dsin.tostring("f3")); catch Console.WriteLine("Invalid input."); Console.Write("\n\n\nPress any key to exit..."); Console.ReadKey(); //Main

9 9 Question 3 static void Main(string[] args) Random rnd = new Random(); Question 4 Console.Write("How many random numbers: "); int n = int.parse(console.readline()); int nodd = 0, neven = 0; for (int i = 1; i <= n; i++) int r = rnd.next (1001 ); if (r % 2 == 0) neven++; else nodd++; double dpercentodd = nodd * / n; double dpercenteven = neven * / n; Console.WriteLine("Percentage even numbers : " + dpercenteven.tostring("0.00")); Console.WriteLine("Percentage odd numbers : " + dpercentodd.tostring("0.00")); Console.Write("\n\nPress any key to continue..."); Console.ReadKey(); private static bool IsPrime(int inumber ) bool isprime = true; //Accept the number is prime until it can be proven to be false int i = 2; //Step through potential factors, i.e. integers less than the number //- Not necessary to search past SQRT(number) //- Stop loop execution as soon as it is found that a number is not prime. while ((i <= Math.Sqrt(iNumber)) && isprime) if (inumber % i == 0) //If number can be divided by a potential factor isprime = false; // without a remainder, is is not prime i++; //Try next potential factor return isprime;