C-DAC Aptitude Test Questions and Answers 2026

Introduction

The C-DAC written aptitude test is the first and most critical filter in both the C-DAC direct recruitment process and the C-CAT (C-DAC Common Aptitude Test) cycle. Every year, thousands of engineering graduates and diploma holders attempt this test, and the majority are eliminated at this stage alone, not because the exam is impossible, but because most candidates underestimate the breadth and technical depth required to clear it comfortably. A focused, section-wise preparation strategy built around the actual test structure makes the difference between struggling at the cutoff and clearing with a strong percentile.

Unlike a general campus placement test, the C-DAC aptitude exam is uniquely demanding in its technical section. While the quantitative, verbal, and reasoning sections are at par with standard engineering placement tests, the 45-question technical section on core computer science topics demands the kind of conceptual depth that only systematic study of operating systems, database management, computer networks, C/C++ programming, and data structures can provide. Half-hearted preparation for the technical section is the most common reason otherwise capable candidates fail to make the shortlist.

This guide is designed specifically around the C-DAC aptitude test structure for 2026, covering all four sections in detail with fully solved examples, section-specific strategies, negative marking guidance, and a section-by-section preparation approach. Whether you are targeting C-DAC direct recruitment as a Project Engineer, Research Engineer, or Software Developer, or preparing for C-CAT to gain admission to C-DAC's PG Diploma courses, this material provides the breadth of coverage you need for both pathways.

C-DAC Aptitude Test Exam Pattern 2026

The C-DAC aptitude test follows a structured multi-section format with a strict time limit and negative marking. Understanding the weight of each section and the implications of negative marking on your answering strategy is as important as knowing the content itself.

Note: Negative marking of -0.25 marks per wrong answer applies across all sections. Total marks: 100 (1 mark per question). Cutoff typically ranges from 50–65 marks depending on the position applied for and the batch difficulty. Time per question is exactly 1 minute on average, speed and accuracy together determine your score. Do NOT guess on technical questions you are uncertain about; the -0.25 penalty makes blind guessing a losing strategy.

Quantitative Aptitude Questions

The quantitative section gives you exactly 1 minute per question. Questions are drawn from standard arithmetic topics taught at Class 10–12 level, but speed matters as much as accuracy. The safest approach: attempt all questions you are certain about first, then return to time-consuming ones. Never spend more than 90 seconds on any single question in this section.

Q1. Two numbers are in the ratio 4:7. If their LCM is 168, find their sum.

Explanation: Let the numbers be 4k and 7k. Since the GCD of 4 and 7 is 1, their LCM = 4 × 7 × k = 28k. Given 28k = 168, k = 6. The numbers are 4×6 = 24 and 7×6 = 42. Sum = 24 + 42 = 66.

Q2. A man walks at 5 km/h and a woman walks at 7 km/h. They start walking towards each other from points 48 km apart. In how many hours will they meet?

Explanation: Relative speed = 5 + 7 = 12 km/h. Time = Distance / Relative Speed = 48 / 12 = 4 hours.

Q3. A sum of money at simple interest doubles in 8 years. In how many years will it become 5 times itself?

Explanation: If principal = P, it becomes 2P in 8 years, so interest earned = P in 8 years. Rate = P/(P×8) × 100 = 12.5% per year. To become 5P: interest needed = 4P. Time = 4P / (P × 12.5%) = 4 / 0.125 = 32 years.

Q4. The average of 5 consecutive even numbers is 28. What is the largest of these numbers?

Explanation: Let the numbers be n, n+2, n+4, n+6, n+8. Average = (5n+20)/5 = n+4 = 28. So n = 24. Largest = 24+8 = 32.

Q5. A boat covers 40 km upstream in 5 hours and 40 km downstream in 2.5 hours. What is the speed of the stream?

Explanation: Upstream speed = 40/5 = 8 km/h. Downstream speed = 40/2.5 = 16 km/h. Speed of stream = (16 - 8)/2 = 4 km/h.

Q6. In a mixture of 80 litres, milk and water are in ratio 3:1. How much water must be added to make the ratio 3:2?

Explanation: Current mixture: milk = 60L, water = 20L. Required ratio 3:2 means water should be (2/3) × 60 = 40L. Water to add = 40 - 20 = 20 litres.

Q7. What is 15% of 25% of 640?

Explanation: 25% of 640 = 160. 15% of 160 = 24.

Verbal Ability Questions

The verbal section is the shortest in both question count and time. Most engineering candidates underestimate this section and score poorly due to inattention to grammar rules and vocabulary. Attempting this section carefully in under 12 minutes (leaving 3 minutes as buffer) is a good strategy, given the easy-medium difficulty.

Q1. Spot the grammatical error: "Each of the students have submitted their assignment on time."

Q2. Choose the word most opposite in meaning to "Lucid":

(a) Clear (b) Transparent (c) Obscure (d) Vivid

Q3. Fill in the blank: The new algorithm was ________ enough to handle edge cases that had previously caused system crashes.

(a) fragile (b) robust (c) archaic (d) redundant

Q4. Rearrange the sentences to form a coherent paragraph: (P) This allows them to switch between tasks rapidly. (Q) Modern operating systems use context switching. (R) Each process stores its state before yielding the CPU. (S) The result is the illusion of parallel execution on a single core.

Q5. Choose the correct sentence: (a) Neither the manager nor the employees was present. (b) Neither the manager nor the employees were present. (c) Neither the manager nor the employees is present. (d) Neither the manager nor the employees has present.

Q6. Identify the passive voice equivalent: "The system administrator configured the server."

Q7. Choose the synonym of "Obsolete":

(a) Modern (b) Outdated (c) Functional (d) Essential

Logical Reasoning Questions

The reasoning section contains the most varied question types in the C-DAC aptitude test. Syllogisms, coding-decoding, number series, blood relations, and seating arrangements are all fair game. Practice each type individually before attempting mixed tests.

Q1. In a certain code, "PROGRAM" is written as "QSPHSBN". What does "DATA" translate to?

Explanation: Each letter is shifted one position forward in the alphabet: P→Q, R→S, O→P, G→H, R→S, A→B, M→N. Applying to DATA: D→E, A→B, T→U, A→B = EBUB.

Q2. All cats are animals. Some animals are birds. Conclusions: (I) Some cats are birds. (II) All animals are cats. Which conclusion(s) follow?

Explanation: From "All cats are animals" + "Some animals are birds", we cannot conclude that any cats are birds (the birds may be in the part of animals that are not cats). Conclusion II is clearly wrong as it reverses the universal statement.

Q3. Find the next number in the series: 3, 9, 27, 81, 243, ?

Explanation: Each term is 3 times the previous term. 243 × 3 = 729.

Q4. A is the mother of B. B is the sister of C. D is the husband of A. How is D related to C?

Explanation: A is the mother of both B and C, since B is described as C's sister, they share the same parent, A. D is the husband of A, which makes D the father of C.

Q5. Six people, A, B, C, D, E, F, sit in a row. A is to the left of B but to the right of C. D is to the right of E but to the left of F. B is at the rightmost position. D is not adjacent to A. Determine the arrangement.

Q6. If 6 January 2026 is a Wednesday, what day will 15 March 2026 be?

Explanation: From 6 January to 15 March is 25 remaining days in January, plus 28 days in February (2026 is not a leap year), plus 15 days in March, a total of 68 days later. 68 mod 7 = 5, so the answer is 5 days after Wednesday, which is Monday.

Q7. If A = 1, B = 2, ..., Z = 26, what is the numerical value of "CODE"?

Explanation: C=3, O=15, D=4, E=5. Most C-DAC-style papers phrase this as a sum-of-values question: 3 + 15 + 4 + 5 = 27. If the question instead asks for positional concatenation, the answer would be written as 3-15-4-5.

Technical Questions

This is the most critical section of the C-DAC aptitude test. With 45 questions in 45 minutes, you have exactly 1 minute per question on average. The technical section covers six major domains: Operating Systems, Database Management Systems, Computer Networks, C and C++ Programming, Data Structures and Algorithms, and Software Engineering. Allocate your preparation proportionally, CS majors should spend at least 60% of their total preparation time on this section.

Q1, Operating Systems. In a Round Robin scheduling algorithm with time quantum of 4ms, processes P1 (burst time 8ms), P2 (burst time 4ms), P3 (burst time 6ms) arrive at time 0. What is the average waiting time?

Explanation: Execution order under Round Robin with quantum 4ms: P1(0–4), P2(4–8), P3(8–12), P1(12–16), P3(16–18). P1 completes at 16 with burst 8, so turnaround time = 16 and wait = 16-8 = 8ms. P2 completes at 8 with burst 4, turnaround = 8, wait = 8-4 = 4ms. P3 completes at 18 with burst 6, turnaround = 18, wait = 18-6 = 12ms. Average wait = (8+4+12)/3 = 24/3 = 8 ms.

Q2, Operating Systems. What is thrashing in the context of virtual memory?

Q3, DBMS. What is the difference between DELETE, TRUNCATE, and DROP in SQL?

• DELETE: DML command. Removes rows one at a time with logging. Can be rolled back. WHERE clause can be used to delete specific rows. Triggers fire. Does not release storage space immediately.
• TRUNCATE: DDL command. Removes all rows at once by deallocating data pages. Cannot be rolled back in most DBMS (no WHERE clause). Faster than DELETE. Resets identity column. Triggers do NOT fire.
• DROP: DDL command. Removes the entire table structure, schema, data, indexes, constraints, permanently. Cannot be rolled back.

Q4, DBMS. Consider the relation R(A, B, C, D) with functional dependencies: A → B, B → C, A → D. Which normal form is this relation in, and what violation exists?

Q5, Computer Networks. What is the difference between a hub, a switch, and a router?

• Hub: Layer 1 (Physical) device. Broadcasts all incoming data to every connected port. No intelligence. Creates a single collision domain.
• Switch: Layer 2 (Data Link) device. Forwards frames based on MAC addresses. Maintains a MAC address table. Each port is a separate collision domain. More efficient than a hub.
• Router: Layer 3 (Network) device. Forwards packets based on IP addresses. Connects different networks. Performs routing protocol computations. Each interface is a separate network.

Q6, Computer Networks. What is the purpose of the ARP protocol? What is ARP cache poisoning?

Q7, C Programming. What will the following code output?

#include <stdio.h>
int main() {
    int x = 5;
    printf("%d %d %d\n", x++, ++x, x);
    return 0;
}

Explanation: Modifying a variable (x) more than once between sequence points is undefined behavior in C. The order of evaluation of function arguments is not specified by the C standard. Compilers may produce different outputs. In exams, the expected answer is often "undefined behavior", choosing this answer demonstrates genuine C knowledge over guessing an output.

Q8, C Programming. What is the output of this program?

#include <stdio.h>
int main() {
    char arr[] = "CDAC";
    printf("%d\n", sizeof(arr));
    return 0;
}

Explanation: sizeof returns the size in bytes of the array including the null terminator '\0'. "CDAC" has 4 characters + 1 null terminator = 5 bytes. Note: if the declaration were char *arr = "CDAC", sizeof would return the size of the pointer (4 or 8 bytes depending on architecture).

Q9, C++ OOP. What is a virtual destructor and why is it needed?

class Base {
public:
    virtual ~Base() { /* cleanup */ }
};
class Derived : public Base {
    int* data;
public:
    Derived() { data = new int[100]; }
    ~Derived() { delete[] data; } // Called correctly with virtual destructor in Base
};

Q10, Data Structures. What is the time complexity of building a heap from an unsorted array of n elements?

Explanation: Intuitively it seems O(n log n) since inserting n elements one by one into a heap is O(n log n). However, the Floyd's heap construction algorithm builds a heap bottom-up by calling heapify on each non-leaf node. The analysis shows that the sum of heapify operations converges to O(n) because most nodes are near the bottom of the heap where heapify costs are minimal. This is a classic exam trap, the correct answer is O(n), not O(n log n).

Q11, Data Structures. Compare Binary Search Tree (BST) and AVL Tree.

Q12, Software Engineering. What is the difference between verification and validation in software testing?

• Verification: "Are we building the product right?", Checking that the software meets its specified requirements. Static process, reviews, walkthroughs, inspections. Example: code review against design specification.
• Validation: "Are we building the right product?", Checking that the software meets the actual user needs. Dynamic process, actual testing with the running software. Example: user acceptance testing.

Boehm's summary: Verification = "Are you doing it right?" Validation = "Are you doing the right thing?"

Q13, Software Engineering. What is cyclomatic complexity? How is it calculated?

Q14, Computer Networks. Calculate the maximum throughput of TCP if the window size is 64 KB and RTT is 50ms.

Explanation: Throughput = Window Size / RTT = (64 × 1024 × 8 bits) / (0.05 seconds) = 524,288 / 0.05 = 10,485,760 bps ≈ 10.24 Mbps.

Q15, OS. What is the difference between paging and segmentation?

• Paging: Physical memory is divided into fixed-size frames; logical memory into same-size pages. Eliminates external fragmentation but causes internal fragmentation. No logical view of the program structure.
• Segmentation: Memory is divided into variable-size segments corresponding to logical program units (code, stack, heap, data). Preserves logical structure but causes external fragmentation.
• Segmentation with Paging: Combined approach (used in x86 architecture), segments are then paged, combining logical view with elimination of external fragmentation.

Interview Process at C-DAC

The aptitude test is Stage 2 in the overall C-DAC recruitment process. Here is the complete multi-stage process for direct recruitment to understand where the aptitude test fits:

• Stage 1, Online Application: Applications submitted via C-DAC's recruitment portal. Eligibility: B.Tech/BE in CS, IT, Electronics, ECE, or equivalent. Academic cutoff: typically 60% throughout (10th, 12th, graduation). No active backlogs.
• Stage 2, Aptitude Test (Written Test): The 100-question, 100-minute MCQ test detailed in this guide. This is the primary mass-filter. Based on performance, candidates are shortlisted for interview stages. Typically 3–5 candidates are called per seat after this filter.
• Stage 3, Technical Interview Round 1: Face-to-face or video interview with a C-DAC technical panel. Questions on the same topics as the technical aptitude section, but in greater depth. Project work is discussed here.
• Stage 4, Technical Interview Round 2 (for research/senior roles): Deeper technical discussion. May include whiteboard coding or architecture design questions.
• Stage 5, HR Interview: Background, career goals, service bond discussion, location preferences.
• Stage 6, Document Verification and Medical: Standard for government/PSU recruitment.

Tips to Crack C-DAC Interview

• Sectional strategy for the aptitude test: Allocate your 100 minutes wisely. Technical section has 45 questions, start there if it's your strongest area. Do not let the aptitude section eat into technical time by over-spending on difficult quant problems.
• Negative marking arithmetic: With -0.25 penalty, you need to be right 4 out of 5 guesses just to break even. Guessing when you have no idea costs you. Only attempt questions where you can eliminate at least two of four options confidently.
• Attempt ordering: Many toppers recommend: Verbal (fastest, easiest) → Reasoning → Quantitative → Technical. This ensures you complete all easier sections and leave maximum remaining time for technical.
• The technical section is the differentiator: The average aptitude scores are clustered. It's the technical section that separates shortlisted candidates from the rest. Spend at least 20 days of focused preparation on OS, DBMS, CN, and C programming before the test date.
• Use C-CAT previous papers religiously: C-CAT papers (available on the official C-DAC website and multiple preparation portals) are the closest available proxy for C-DAC's direct recruitment aptitude test. Solve at least 5 full-length previous papers under timed conditions.
• Flashcards for technical facts: Many technical questions test specific facts, port numbers (HTTP=80, HTTPS=443, FTP=21, SSH=22), OSI layer functions, SQL command categories (DDL/DML/DCL/TCL), or complexity of algorithms. Flashcards reviewed daily help retain these efficiently.
• Do not skip Software Engineering: SE questions (SDLC models, testing types, McCabe's metric, UML diagrams) appear regularly in the C-DAC technical section and are frequently neglected by candidates who focus only on programming and OS. Each SE question you answer correctly is worth as much as an OS question.
• Mock tests under strict timing: Practise at least 3 full-length mock tests in the exact timed format, 100 questions in 100 minutes. Do not pause. After each test, review every wrong answer and understand the correct reasoning.
• Paper-based practice for aptitude: Even though the exam is online, practising quantitative and reasoning problems on paper improves mental math and forces you to show your working, which helps spot calculation errors.
• Focus on accuracy over speed in final 2 weeks: In the last two weeks before the exam, shift from solving maximum problems to solving problems with 95%+ accuracy. Wrong answers hurt more than unattempted questions.

Common HR Interview Questions

Q1. Why do you specifically want to join C-DAC over private software companies?

Sample Answer: C-DAC works at the intersection of advanced technology and national impact, the PARAM supercomputer family, embedded systems for defense, indigenous software stacks. That kind of work is not available at a product company or an IT services firm at the fresher level. I want to build my technical career on problems that are hard at a systems level, not just at an application level, and C-DAC is genuinely the best place in India to do that.

Q2. Tell me about your final year project.

Sample Answer: Prepare this cold. Know every line of code, every design decision, every tradeoff you made. C-DAC interviewers will probe: Why did you choose this algorithm? How would you scale it? What would you change now? Candidates who understand their own projects deeply impress C-DAC panels because it shows engineering rigor, not just project completion.

Q3. What is your understanding of the difference between C-DAC recruitment and C-CAT?

Sample Answer: C-CAT is the entrance exam for C-DAC's PG Diploma programs, intensive courses at CDAC-ACTS and other C-DAC centres that upskill candidates in embedded systems, VLSI, cloud computing, data science, and other advanced domains. C-DAC direct recruitment, which I am pursuing, is for employment as a Project Engineer or Research Engineer directly contributing to C-DAC's R&D projects and contracts. Both pathways involve similar technical domains, but the outcomes are different, one is education, the other is employment.

Q4. Are you comfortable with the C-DAC service bond?

Sample Answer: Yes. I understand that C-DAC invests significantly in training and onboarding new engineers for specialised R&D work, and the bond reflects that investment. I am committed to the work here and am not approaching this role as a short-term stepping stone. I want to build substantive technical expertise in this environment, and the bond aligns with that intention.

Q5. What area of computer science excites you most and how does it connect to C-DAC's work?

Sample Answer: Operating systems and embedded systems programming excite me most, the challenge of building reliable, efficient software with constrained resources is fundamentally different from application development. C-DAC's work on real-time operating systems for embedded applications, and the PARAM HPC systems that require low-level systems programming, are exactly where I want to contribute. I have done coursework on OS internals and built a mini-shell as a course project, which gave me a concrete sense of how interesting this domain is.

Salary Package Information

The figures below are candidate-reported and indicative only. C-DAC roles follow government pay structures that are revised by pay commission cycle and vary by centre and role, so confirm the exact numbers against the official C-DAC recruitment notification for your applied post.

Additional Benefits: Government benefits apply, HRA, medical coverage under CGHS, provident fund, gratuity, LTC (Leave Travel Concession), study leave for further education, and access to C-DAC's internal certification programs. Salary revision follows government pay commission cycles. Job security is a significant non-monetary benefit compared to private sector volatility.

Preparation Strategy

Days 1–7, Technical Foundation, OS and DBMS: Revise OS concepts: process management, scheduling, memory management, deadlocks, file systems. For DBMS: normalization, SQL, transactions, ACID properties, indexing, joins. Use short notes after each topic. Target: be able to answer 35 of the 45 technical questions from these two topics alone.

Days 8–14, Technical Foundation, CN and C/C++: Computer Networks: OSI model, TCP/IP, protocols layer-by-layer, subnetting, routing, common port numbers. C Programming: pointers, arrays, strings, structures, dynamic memory, file I/O, common programs (sort, search, string manipulation). C++: OOP pillars, virtual functions, templates, STL basics.

Days 15–18, Data Structures and Algorithms: Revise all major DS: arrays, linked lists, stacks, queues, trees (BST, AVL), heaps, graphs, hash tables. Know time/space complexities. Sorting algorithms: bubble, selection, insertion, merge, quick, heap sort. Graph algorithms: BFS, DFS, Dijkstra.

Days 19–21, Software Engineering and Aptitude Sections: SE: SDLC models (Waterfall, Agile, Spiral), testing types, cyclomatic complexity, UML basics, design patterns (Factory, Singleton, Observer). Quantitative: 30 questions per day from time-work, percentages, series, geometry. Verbal: 15 minutes daily on grammar rules and vocabulary.

Days 22–25, Reasoning and Sectional Practice: Complete logical reasoning topics: series, coding-decoding, blood relations, syllogisms, seating arrangements. Timed sectional tests, do each section individually under strict time constraints before combining.

Days 26–30, Full Mock Tests and Revision: Three complete full-length mock tests on Days 26, 28, and 30. Review every incorrect answer. Light revision of weakest topics. Prepare a one-page cheat sheet of key technical facts (port numbers, SQL commands, complexity values, OS formulas) for final-day review.

Conclusion

The C-DAC aptitude test is winnable with the right preparation strategy, but it punishes candidates who prepare narrowly. The combination of a reasonably competitive aptitude section and a highly technical 45-question CS section means you cannot afford to focus only on quant puzzles and vocabulary drills, the technical section is where the real competition happens and where most seats are truly won or lost.

Treat the negative marking as a strategic variable, not just a penalty clause. Knowing when not to answer is as important as knowing the correct answer. Candidates who understand this and build their test-taking strategy around it consistently outperform peers with similar content knowledge who guess liberally.

Finally, the C-DAC aptitude test should be seen as the beginning of your C-DAC journey, not the destination. The technical interviews that follow require the same conceptual depth, but applied conversationally and under direct challenge. Candidates who prepare the aptitude test with genuine understanding, not just pattern-matching to previous papers, find that the interview rounds feel like a natural continuation rather than a new challenge entirely.

This article is part of PapersAdda's comprehensive placement preparation series. For more interview guides, aptitude questions, and company-specific preparation material, explore our full library at PapersAdda.

FAQ

What is the pattern of the C-DAC aptitude test in 2026?

The C-DAC aptitude test has four sections totaling 100 questions in roughly 100 minutes: Quantitative Aptitude (20 questions, 20 minutes), Verbal Ability (15 questions, 15 minutes), Logical Reasoning (20 questions, 20 minutes), and Technical/Core CS (45 questions, 45 minutes). Each wrong answer carries a 0.25 mark penalty. Confirm the current pattern on the official C-DAC portal, as timing and question counts can vary by recruitment cycle.

What is the cutoff for the C-DAC aptitude test?

C-DAC does not publish an official cutoff. Candidate reports suggest scores typically range from 50 to 65 out of 100 depending on the position applied for and batch difficulty, but this is an inferred pattern, not a guarantee. Confirm current cutoff trends on the official C-DAC portal or recruitment notification.

Which section of the C-DAC aptitude test matters most?

The Technical/Core CS section, 45 of the 100 total questions, covering operating systems, DBMS, computer networks, C/C++ programming, and data structures, is what candidate reports describe as the real differentiator, since quantitative, verbal, and reasoning scores tend to cluster closely across candidates. Prioritizing technical preparation is the most commonly recommended strategy.

Is there negative marking in the C-DAC aptitude test?

Yes. Candidate reports describe a uniform penalty of 0.25 marks for every wrong answer across all four sections. Because 4 wrong guesses cancel out the value of roughly 1 correct answer, the commonly recommended strategy is to attempt a question only when you can confidently eliminate at least two of the four options.

How is the C-DAC aptitude test different from C-CAT?

The C-DAC aptitude test covered in this guide is part of C-DAC's direct recruitment process for roles like Project Engineer and Research Engineer, while C-CAT (C-DAC Common Aptitude Test) is a separate entrance exam for admission to C-DAC's postgraduate diploma programs. The technical content overlaps significantly, so preparation for one substantially helps with the other, but confirm which exam applies to your specific goal on the official C-DAC portal.