Technical aptitude Test 1 CSE

The aptitude test consisted tricky questions on core subjects of CSE like C , C++, Java ,Data Structures, Database, Computer Networks, Theory of Computation.

1. Walchand College Of Engineering,Sangli ORGANIZES Technical Aptitude Test ASSOCIATION of Computer Science & Engg . STUDENTS Date:21 July,2015 By Sujata Regoti

2. 1 .What will be output when you will execute following c code? #include< stdio.h > void main() { int a=5; a=a >=4; switch(2) { case 0:int a=8 ; case 1:int a=10 ; case 2:++a ; case 3:printf("% d",a ); } } 2 10 C. Compilation error D. no output E x p l a n a t i o n : We can not declare any variable in any case of switch case statement. 1

3. 2 .What is the infix version of the following postfix expression? x 12 + z 17 y + 42 * / +   A. (x + 12 + z) / (17 + y * 42) B. x + 12 + z / 17 + y * 42 C. x + 12 + z / (17 + y) * 42 D. x + 12 + z / ((17 + y) * 42) E. x + (12 + z) / (17 + y * 42) 2

4. 3 . If we use mergesort to sort an array with n elements, what is the worst case time required for the sort ? A. O(1) B. O(log n) C. O(n) D. O(n log n) E. O(n2) 1

5. 4.Output of following C ++ code is int &check() { static int num = 30; return num ; } int main() { check () = 40; cout << check (); return 0; } A.Compiler Error: lvalue required B.40 C.30 D.0 Exp : When a function returns by reference, it can be used as lvalue . Since x is a static variable , every call to fun() will not assign 30 1

6. 5.Output of following C++ code is (consider int 4 bytes) #include < stdio.h > int cse ; int main() { struct cse { double x; }; printf ("%d", sizeof ( cse )); return 0; } A. 8 B. 2 C. 4 D. Compiler error Expl : In cpp struct keyword not required to use with variable name. So cse hides global variable cse 1

7. 6 .What is output of following C ++ code #include< iostream > class Test { public : int s; Test( int s){ this->s=s ; } static Test & fun() { return this; } }; int main() { Test t1(20),t2(30); t2=t1.fun(); std :: cout << t2.s; } A.20 B. Compilation error C.30 D. Runtime error //error : this is unavailable for static member functions 1

8. 7.What is the output for the below java code ? public class Test{ int _$; int $7; int do; public static void main(String argv []){ Test test = new Test(); test.$7=7; test.do=9;   System.out.println (test.$7); System.out.println (test.do); System.out.println (test._$); } } A.7 9 0 B.7 0 0 C.Compile error - $7 is not valid identifier. D.Compile error - do is not valid identifier . Expl : do is keyword 1

9. 8. What is expected output public class Test { public static void main(String[] args ) { String s=null; System.out.println ( null+s ); } } A.Runtime Exception thrown B.null C.nullnull D.Compiler error 1

10. 9.What is expected output public static void main(String[] args ) { String s=""; StringBuffer sb =""; int i=5; if(i<0) s.concate ("java rock"); else sb.append ("java rock"); System.out.println ( s+sb ); } A.javarock B.javarock javarock C.Compilation error D.No output E.Runtime error Exp. :We cant directly assign string to stringbuffer So Error :incompatible types at Line StringBuffer sb =“”; It should be sb =new StringBuffer (“”); 2

11. 10. How can this program be modified to make use of appropriate generic types? (one modification for each line) //Choose 3 options import java.util .*; public class Test { public static void main(String[] args ) { List ids = new ArrayList (); // Line 1 ids.add (123); ids.add (999); Map students = new HashMap (); // Line 2 students.put ("Jess", ids.get (0)); students.put ("Jimmy", ids.get (1 )); int x = ((Long) students.get ("Jimmy")). intValue (); // Line3 } } A. replace line 1 with List<Integer> ids = new ArrayList <Integer>(); B. replace line 1 with List<Long> ids = new ArrayList <Long>(); C. replace line 2 with Map< Integer,String > students = new HashMap < Integer,String >(); D. replace line 2 with Map< String,Integer > students = new HashMap < String,Integer >(); E. replace line 3 with int x = students.get ("Jimmy"); 2

12. 11. class Test { public static void main(String[] args ) { Integer i = new Integer(0); Float f = new Float(0); System.out.println (i==f); System.out.println ( i.equals (f)); } } O/p is:   true false false true true true Compiler error Explanation : error: incomparable types:Integer and Float 1

13. 12. Which of the following are not a valid declarations ? A . float f = 1; B . float f = 1.2f; C . float f = 1.2; float f = ( float)1.2; Explanation : By Default real number is double which cant be directly assigned to float . So 3 rd declaration throws error : possible loss of precision occur. 1

14. 13. A process executes the code fork(); fork(); fork(); The total number of child processes created is A. 8 B . 7 C . 6 D . 3 2

15. 14.Which of the following memory allocation scheme suffers from external fragmentation ? A. Segmentation B. Pure demand paging C. Swapping D. Paging Explanation : External fragmentation occurs in systems that use pure segmentation.Because each segment has varied size to fit each program size, the holes (unused memory) occur external to the allocated memory partition. 1

16. 15.Which of the following concurrency control protocols ensure both conflict serializability and freedom from deadlock? I. 2-phase locking II. Time-stamp ordering A. I only B . II only C. Both I and II D. Neither I nor II 2 Phase Locking (2PL) is a concurrency control method that guarantees serializability . The protocol utilizes locks, applied by a transaction to data, which may block (interpreted as signals to stop) other transactions from accessing the same data during the transaction’s life. 2PL may be lead to deadlocks that result from the mutual blocking of two or more transactions. See the following situation, neither T3 nor T4 can make progress. Timestamp-based concurrency control algorithm is a non-lock concurrency control method. In Timestamp based method, deadlock cannot occur as no transaction ever waits. 1

17. 16.Consider the following relational schema: Employee ( empId , empName , empDept ) Customer ( custId,custName , salesRepId , rating) SalesRepId is a foreign key referring to empId of the employee relation. Assume that each employee makes a sale to at least one customer. What does the following query return? SELECT empName FROM Employee E WHERE NOT EXISTS (SELECT custId FROM customer C WHERE C. salesRepId = E. empId AND C. rating < > ‘GOOD’)   Names of all the employees with at least one of their customers having a ‘GOOD ’ rating. B . Names of all the employees with at most one of their customers having a ‘ GOOD’ rating. C . Names of all the employees with none of their customers having a ‘ GOOD’ rating. D . Names of all the employees with all their customers having a ‘GOOD’ rating . 2

18. 16. Explanation The outer query will return the value (names of employees) for a tuple in relation E, only if inner query for that tuple will return no tuple (usage of NOT EXISTS). The inner query will run for every tuple of outer query. It selects cust -id for an employee e, if rating of customer is NOT good. Such an employee should not be selected in the output of outer query. So the query will return the names of all those employees whose all customers have GOOD rating. 2

19. 17.Consider different activities related to email. m1:Send an email from a mail client to mail server m2:Download an email from mailbox server to a mail client m3:Checking email in a web browser Which protocol is applicable in each activity ? A. m1:HTTP, m2:SMTP, m3:POP B . m1:SMTP, m2:FTP, m3:HTTP C. m1:SMTP, m2:POP, m3:HTTP D. m1:POP, m2:SMTP, m3:IMAP Simple Mail Transfer Protocol (SMTP) is typically used by user clients for sending mails. Post Office Protocol (POP) is used by clients for receiving mails. Checking mails in web browser is a simple HTTP process. 1

20. 18. A layer-4 firewall ( a device that can look at all protocol headers up to the transport layer) CANNOT A . block HTTP traffic during 9:00PM and 5:00AM B. block all ICMP traffic C. stop incoming traffic from a specific IP address but allow outgoing traffic to same IP D. block TCP traffic from a specific user on a specific IP address on multi-user system during 9:00PM and 5:00AM Exp : HTTP is an application layer protocol. Since firewal is at layer 4, it cannot block HTTP data. 1

21. 19.Consider the following languages over the alphabet S = {0,1,c} L1={ 0^n 1^n | n>=0} L2={ wcw^r |w ∈ {0,1}*} L3={ ww^r |w ∈ {0,1}*} Here w^r is the reverse of the string w. Which of these languages are deterministic Context free languages ? A . None of the languages B . Only L1 C . Only L1 and L2 D . All the three languages Exp:For the languages L1 and L2 we can have deterministic push down automata, so they are DCFL’s, but for 3 L only non-deterministic PDA possible. So the language L3 is not a deterministic CFL. 1

22. 20.The number of states in the minimal deterministic finite automaton corresponding to the regular expression (0+1)*(10) is A . One B . Three C . Four D . Two 1