Karnataka CST Previous Year Question Papers PDF with Answers

CST previous year questions with answers

These are the questions in the PDF. Tap “Show answer” to check yourself.

1. The output of an AND gate with three inputs P, Q and R is HIGH when

   1. P = 1, Q = 1, R = 0
   2. P = 0, Q = 0, R = 0
   3. P = 1, Q = 1, R = 1
   4. P = 1, Q = 0, R = 1

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: C. P = 1, Q = 1, R = 1

   • An AND gate gives output 1 (HIGH) only when every input is 1.
   • If any one input is 0, the output is 0 (LOW).
   • Only P = 1, Q = 1, R = 1 makes P · Q · R = 1.

2. A powerset is the set of all subsets of a given set of n elements. How many such subsets of 2 elements are present in the powerset?

   1. n²/2
   2. 2n
   3. n(n − 1)/2
   4. n²

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: C. n(n − 1)/2

   • A subset of 2 elements is a choice of 2 elements out of n, order not mattering.
   • The number of such choices is nC2 = n!/(2!(n − 2)!).
   • This simplifies to n(n − 1)/2; e.g. n = 4 gives 6 two-element subsets.

3. The minimum number of edges required to create a cyclic graph of N vertices are

   1. N
   2. N + 1
   3. N – 1
   4. 2N

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: A. N

   • A connected graph on N vertices with N – 1 edges is a tree, and a tree has no cycle.
   • Adding one more edge between two already-connected vertices always creates a cycle.
   • So N edges are the minimum for a connected cyclic graph on N vertices, for example a single cycle through all N vertices.

4. Two graphs G1 and G2 are said to be isomorphic if

   1. Their number of vertices and edges are the same and their edge connectivity is retained
   2. Their number of vertices and edges are the same but their edge connectivity may not be retained
   3. The number of vertices is the same and the edges may differ
   4. The number of vertices may differ but the edges should be the same

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: A. Their number of vertices and edges are the same and their edge connectivity is retained

   • Isomorphic graphs are the same graph drawn with different vertex names.
   • There must be a one-to-one mapping of vertices that preserves adjacency (edge connectivity).
   • So both graphs have equal numbers of vertices and edges, and connections are kept.
   • Equal counts alone are not enough if the edge connections are not preserved.

5. The time complexity required to search a key in a binary search tree of height h is

   1. O(h³)
   2. O(h²)
   3. O(h)
   4. O(h log h)

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: C. O(h)

   • Searching a BST starts at the root and moves one level down at each comparison.
   • At most one node per level is visited, so at most h + 1 comparisons are made.
   • Hence search takes O(h); this is O(log n) for a balanced tree and O(n) for a skewed one.

6. What kind of register can have a complete binary number loaded into it in one operation, and then have it shifted out one bit at a time?

   1. Serial in/Parallel out
   2. Parallel in/Parallel out
   3. Serial in/Serial out
   4. Parallel in/Serial out

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: D. Parallel in/Serial out

   • Loading all bits in one operation is a parallel input.
   • Shifting the bits out one at a time is a serial output.
   • A PISO (Parallel In/Serial Out) shift register does exactly this.
   • It is used for parallel-to-serial conversion, e.g. before sending data over a serial line.

7. Anarkali digitally signs a message and sends it to Salim. Verification of the signature by Salim requires

   1. Anarkali's public key
   2. Salim's public key
   3. Salim's private key
   4. Anarkali's private key

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: A. Anarkali's public key

   • The sender signs a message with the sender's own private key.
   • Anyone can verify the signature with the sender's public key.
   • So Salim needs Anarkali's public key; her private key is never shared.

8. The Schmitt trigger may be used to

   1. Change voltage to corresponding frequency
   2. Change frequency to voltage
   3. Square slowly varying input
   4. Change voltage to frequency

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: C. Square slowly varying input

   • A Schmitt trigger is a comparator with hysteresis: it switches at an upper threshold and switches back at a lower one.
   • A slowly changing or noisy input therefore produces clean, sharp transitions at the output.
   • This turns a slowly varying input (such as a sine wave) into a square wave; voltage-frequency conversion needs a VCO or a V/F converter instead.

9. In inheritance,

   1. when a virtual function is inherited, the virtual nature of a virtual attribute cannot be inherited
   2. the virtual function can be overridden
   3. when a virtual function is inherited, it does not remain virtual
   4. when a derived class is inherited, a virtual function cannot be used as a base class for another derived class

   From: CST 2018 - Specific Paper II (Computer Science)

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   Answer: B. the virtual function can be overridden

   • A virtual function is declared in a base class so that derived classes can override it.
   • Once virtual, a function stays virtual in every derived class, even without the keyword.
   • A call through a base-class pointer or reference then runs the derived class's version (run-time polymorphism).

10. Which of the following ways is legal to access a class data member x using the "this" pointer?

    1. this->x
    2. *this.x
    3. *(this.x)
    4. (*this.x)

    From: CST 2018 - Specific Paper II (Computer Science)

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    Answer: A. this->x

    • In C++, this is a pointer to the current object, so a member is reached with the arrow operator: this->x.
    • this->x means the same as (*this).x — dereference this first, then select x.
    • In *this.x the dot binds tighter than *, so this.x is tried first, which is illegal because this is a pointer.
    • *(this.x) and (*this.x) make the same mistake; only this->x is legal here.

11. A sort which repeatedly passes through a list, exchanging the first element with any element less than it, and then repeats with a new first element is called

    1. Insertion sort
    2. Selection sort
    3. Heap sort
    4. Quick sort

    From: CST 2018 - Specific Paper II (Computer Science)

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    Answer: B. Selection sort

    • In each pass the first position of the unsorted part is compared with every later element.
    • Whenever a smaller element is found it is exchanged into that first position.
    • After the pass the smallest element is fixed there, and the pass repeats from the next position.
    • Selecting the minimum for each position this way is selection sort.

12. The functionality of the Banker's algorithm is

    1. To prevent deadlock
    2. To detect deadlock
    3. To solve deadlock
    4. To rectify deadlock

    From: CST 2018 - Specific Paper II (Computer Science)

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    Answer: A. To prevent deadlock

    • The Banker's algorithm checks every resource request before granting it.
    • A request is granted only if the system stays in a safe state afterwards.
    • This keeps deadlock from ever occurring (deadlock avoidance), so it is used to prevent deadlock.
    • Detection and recovery algorithms act only after a deadlock has happened.

13. In a 1:N relationship, the foreign key is placed in

    1. Either table without specifying parent and child tables
    2. The parent table
    3. The child table
    4. Either the parent table or the child table

    From: CST 2018 - Specific Paper II (Computer Science)

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    Answer: C. The child table

    • In a 1:N relationship one parent row is related to many child rows.
    • A column can hold only one value per row, so the parent cannot store a list of child keys.
    • Each child row stores its single parent's primary key as a foreign key.
    • Hence the foreign key always goes in the child (the 'many' side) table.

14. What device separates a single network into two segments but lets the two segments appear as one to higher protocols ?

    1. Switch
    2. Bridge
    3. Router
    4. Gateway

    From: CST 2018 - Specific Paper II (Computer Science)

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    Answer: B. Bridge

    • A bridge works at the data link layer and splits one LAN into two segments, filtering frames by MAC address.
    • Because it does not change network-layer addressing, both segments remain one network to IP and higher protocols.
    • A router, by contrast, joins separate networks, each with its own network address.

15. A line connecting the points (1, 1) and (5, 3) is to be drawn using the DDA algorithm. Find the values of the x and y increments.

    1. x-increment = 1; y-increment = 1
    2. x-increment = 0.5; y-increment = 1
    3. x-increment = 1; y-increment = 0.5
    4. None of the above

    From: CST 2018 - Specific Paper II (Computer Science)

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    Answer: C. x-increment = 1; y-increment = 0.5

    • dx = 5 − 1 = 4 and dy = 3 − 1 = 2.
    • Steps = max(|dx|, |dy|) = 4.
    • x-increment = dx/steps = 4/4 = 1.
    • y-increment = dy/steps = 2/4 = 0.5.

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• CST 2018 - Specific Paper II (Computer Science)

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