1st Year Computer Science — MCQs & Practice Questions

Requirements gathering, analysis, design, implementation, testing, deployment and maintenance. Different models order or repeat them differently, but these are the stages every project passes through.

A functional requirement states what the system must do — "the system shall calculate each student's attendance percentage". A non-functional requirement states how well it must do it — "each report shall be produced within five seconds".

By deployment the fault is embedded in written code that other parts depend on, users have been trained on the incorrect behaviour, and any damage it caused must also be repaired. During design it costs only a change to a document before anything was built on it.

1. Waterfall completes each stage fully and signs it off before the next begins; iterative repeats the stages in short cycles[1]
2. In waterfall the customer sees working software only at the end; in an iterative model they see something usable every cycle[1]
3. Waterfall suits a project whose requirements are fully known and stable — replacing a well-understood manual process, or a system whose rules are set by law[1]
4. Iterative suits a project whose requirements are uncertain or likely to change, since misunderstandings surface within weeks rather than at the end[1]

Sequential and documented against cyclic and adaptable; waterfall for stable requirements, iterative for uncertain ones.

1. Normal: a 12-character password — acceptedcomfortably inside the range[1]
2. Boundary: 8 characters and 16 characters — both acceptedthe limits are inside the allowed range[1]
3. Boundary: 7 characters and 17 characters — both rejectedcatches > written instead of >=[1]
4. Erroneous: an empty field — rejected with a clear message rather than a crashthe empty case is the one most often missed[1]

Normal 12; boundary 8, 16, 7, 17; erroneous empty.

1. Interviews with teachers and office staff, revealing what information they need and what the current process cannot do[1]
2. Observation of the register being taken, revealing the exceptions and workarounds people no longer notice they use — late arrivals, half days, tripsobservation catches what interviews miss[1]
3. Functional: "the system shall calculate each student's attendance percentage for a chosen date range"a specific, testable action[1]
4. Non-functional: "a monthly report for a class of 40 shall be produced within five seconds"measurable, so it can be tested[1]
5. Acceptance testing decides whether the system does what the customer actually asked for, so only the customer can judge it[1]
6. The developer tests against their own understanding of the requirements — which is precisely what may have been wrong from the startthe circularity is the point[1]

(a) interviews for needs, observation for the unspoken exceptions (b) attendance percentage; report within five seconds (c) only the customer can say whether it does what they meant

A variable is a named location in memory holding a value. x = 10 creates the name x and assigns the integer value 10 to it. Assigning again later replaces the value rather than creating a second variable.

Because input() always returns a string, even when the user types digits. Without conversion, + would join the text instead of adding — "5" + "3" gives "53" — and comparisons would compare text rather than numeric value.

= is the assignment operator, storing a value in a variable. == is the comparison operator, testing whether two values are equal and producing True or False.

1. length = float(input("Enter length: "))float rather than int allows decimal measurements[1]
2. width = float(input("Enter width: "))[1]
3. area = length * widtha meaningful variable name is expected[1]
4. print("The area is", area)output must be labelled, not a bare number[1]

Read both values as floats, multiply, and print with a label.

1. (i) 3 — integer division discards the remaindernot 3.5[1]
2. (ii) 1 — the remainder when 7 is divided by 2[1]
3. (iii) 3.5 — / always produces a floatnote the decimal point[1]
4. (iv) 8 — ** is the power operator2 cubed[1]

(i) 3 (ii) 1 (iii) 3.5 (iv) 8

1. Error 1: the inputs are strings, so they are joined rather than addedint() or float() is missing[1]
2. Error 2: operator precedence — a + b / 2 divides b by 2 first, so brackets are needed: (a + b) / 2this error survives even after the type is fixed[1]
3. Corrected input lines using float(input(…))[1]
4. avg = (a + b) / 2 followed by a labelled print[1]
5. Test with normal data, such as 60 and 80, and check the answer is 70a value you can verify by hand[1]
6. Test with boundary data such as 0 and 100, and with erroneous data such as text, to see how it behavesall three kinds of test data[1]

(a) inputs not converted, and missing brackets (b) float(input(…)) and (a+b)/2 (c) normal, boundary and erroneous data

Sequence — statements written one after another, needing no keyword. Selection — if. Iteration — for or while.

When the number of repetitions is not known in advance and depends on a condition evaluated during the loop — for example repeating until the user enters valid input or types "quit". A for loop is used when the count is fixed beforehand.

Five times, with i taking the values 2, 3, 4, 5 and 6. The upper bound 7 is where the sequence stops and is not itself used.

1. for n in range(1, 21): — the upper bound must be 21 to include 20the off-by-one is examined here[1]
2. if n % 3 == 0:the remainder test for divisibility[1]
3. print(n) correctly indented inside the ifindentation is part of the mark[1]
4. Output: 3, 6, 9, 12, 15, 18[1]

A for loop over range(1, 21) with an if n % 3 == 0 test inside.

1. Nothing inside the loop changes count[1]
2. So the condition count > 0 is true on every pass and never becomes false — an infinite loopnaming it as infinite is expected[1]
3. Add count = count - 1 inside the loopaccept count -= 1[1]
4. It must be indented inside the loop; placed outside it would run only once, after the loopthe indentation point is a mark[1]

The loop variable is never decremented. Add count = count - 1 indented inside the loop.

1. A for loop, because the number of marks is known in advance to be tenthe reason must be given[1]
2. Initialise total = 0 and passes = 0 before the loopaccumulators must start outside the loop[1]
3. for i in range(10): then read a mark and add it to total[1]
4. if mark >= 50: passes = passes + 1, correctly indented inside the loop[1]
5. After the loop: print(passes) and print(total / 10)[1]
6. The prints must be outside the loop, because inside they would run on every pass and print ten partial results instead of one final answerthe reason is the mark[1]

(a) for, since ten is known (b) accumulators before, loop reads and tests, prints after (c) outside, or they print ten partial results

The data must already be sorted. The algorithm discards half the list at each step by comparing with the middle item, which is only valid if the order is known.

A measure of how the number of operations grows as the size of the input grows, written in big-O notation. It describes the trend, not the exact running time on a particular machine.

About 10, because 2¹⁰ = 1024. Each comparison halves the remaining list, so the maximum is log₂ n rounded up.

1. After pass 1: 3, 5, 1, 8[1]
2. After pass 2: 3, 1, 5, 8[1]
3. After pass 3: 1, 3, 5, 8[1]
4. Three passes; a fourth confirms no swaps[1]
5. A flag records whether any swap was made; if a whole pass makes none, the list is sorted[1]
6. O(n²)[1]
7. Doubling the data quadruples the work, so it becomes impractically slow[1]

1. Initialises low = 1 and high = 5000[1]
2. Loops while low <= high[1]
3. Calculates mid = (low + high) DIV 2[1]
4. Compares and returns mid if the name matches[1]
5. Otherwise sets high = mid − 1 or low = mid + 1 correctly[1]
6. Returns a value such as −1 or FALSE once low > high[1]
7. Binary search: at most 13 comparisons, since 2¹³ = 8192[1]
8. Linear search: up to 5000, so binary search is dramatically faster[1]

1. Merge sort or quicksort (average case)[1]
2. The log n factor grows very slowly compared with the extra factor of n[1]
3. So the gap between the two widens rapidly as n increases[1]
4. Doubling n slightly more than doubles n log n[1]
5. So roughly 4.2 to 4.5 seconds, a little over doubleaccept "just over 4 seconds" with reasoning[1]

Advantage: any element can be reached directly from its index in constant time. Disadvantage: inserting at the front requires every later element to be shifted.

A stack is last-in-first-out: items are added and removed at the same end. A queue is first-in-first-out: items are added at one end and removed from the other.

On a push the pointer is incremented and the new item is written at that position. On a pop the item at the pointer is read and the pointer is decremented. The pointer must be checked against the array bounds first.

1. Jobs must be printed in the order they were submitted[1]
2. A queue removes items in the same order they were added, which is first-in-first-out[1]
3. In a linear queue the front pointer moves forward and the space behind it is wasted[1]
4. A circular queue wraps the rear pointer round to the start of the array[1]
5. So the freed space is reused and the array does not appear full while space remains[1]
6. That the queue is not full[1]

1. 50 at the root with 30 on its left and 70 on its right[1]
2. 20 and 40 as the children of 30[1]
3. 60 as the left child of 70[1]
4. Visits left subtree, then node, then right subtree[1]
5. 20, 30, 40, 50, 60, 70[1]
6. The values in ascending order[1]
7. It can therefore be used to sort the data, or to output it in order without re-sorting[1]

(b) 20, 30, 40, 50, 60, 70

1. Traverse from the head until the node after which Chand belongs is found, here Bilal[1]
2. Create the new node and set its pointer to whatever Bilal was pointing at, that is Danish[1]
3. Set Bilal's pointer to the new nodethis order matters or the rest of the list is lost[1]
4. The nodes are not stored in consecutive memory locations[1]
5. Order is held by the pointers, so changing two pointers is enough[1]

Descriptive analytics summarises what has already happened — sales fell 12% last quarter. Predictive analytics uses historical patterns to estimate what is likely to happen next, and its output is a probability rather than a fact.

Structured: a table of student records with fixed columns for name, roll number and marks. Unstructured: free-text comments in a feedback form, or photographs — data with no fixed row-and-column shape.

Because very different situations can share the same average. A mean of 60 is consistent with everyone scoring 60 and with half the class scoring 20 while half scored 100 — and those two situations require completely different responses.

1. A third factor may cause both — a settled home routine could produce both regular breakfasts and regular study[1]
2. Reverse causation is possible — students who are already doing well may be less anxious and therefore more able to eat in the morning[1]
3. The sample may not be representative, or the difference may be small enough to be chance[1]
4. Establishing causation would require a controlled study in which breakfast is the only difference between comparable groupsthe remedy is the fourth mark[1]

A third factor, reverse causation, or chance — only a controlled study could establish a cause.

1. The vertical axis is truncated, starting at 98 rather than 0[1]
2. This magnifies a change of about 4% into what appears to be a dramatic risethe visual slope is unrelated to the real change[1]
3. The axis should start at zero so the height of each point is proportional to its value[1]
4. If a truncated axis is genuinely necessary to show small variation, it must be clearly labelled and the actual percentage change statedthe honest alternative, not simply a prohibition[1]

A truncated axis exaggerates a 4% change. Start at zero, or label the truncation and state the real change.

1. Descriptive: average attendance, the distribution of results, how many students fall below a threshold[1]
2. Diagnostic: whether low results are concentrated in particular classes, subjects or year groups, and whether they coincide with low attendancediagnostic looks for where and why[1]
3. Problem: incomplete or inconsistent data — attendance recorded differently by different teachers, or missing entries treated as zero[1]
4. Problem: correlation misread as causation — low attendance and low marks may both follow from a third cause such as illness or family circumstances[1]
5. A prediction is a statistical statement about a group, not a fact about the individual student[1]
6. Acting on it risks becoming self-fulfilling: a student treated as likely to fail may receive lower expectations and therefore do worsethe self-fulfilling point is the strongest available[1]

(a) distributions and where problems concentrate (b) inconsistent recording, and correlation read as cause (c) a prediction describes a group and can become self-fulfilling

Cloud computing is the delivery of computing resources — storage, processing power, software — over the internet, rented from a provider rather than owned. One advantage is scalability: capacity can be increased for a busy period and reduced afterwards, so you pay only for what you use.

It depends entirely on internet connectivity — an outage stops all work. And the data is stored on hardware the business does not control, raising security and legal questions about who can access it and in which country it is held.

The Internet of Things is the network of everyday physical objects fitted with sensors and network connections, which collect and exchange data automatically. Example: a smart thermostat that reports the temperature and can be adjusted remotely.

1. IoT devices are cheap and produced in huge numbers, and many ship with default passwords that users never change[1]
2. They often receive no security updates after release, so a known vulnerability remains exploitable for the life of the devicethis is the core of the problem[1]
3. Measure: change default credentials immediately and apply any firmware updates the manufacturer provides[1]
4. Measure: place IoT devices on a separate network from computers holding important data, so a compromised device cannot reach themnetwork segmentation[1]

Default passwords and absent updates; fix with changed credentials and a separate network.

1. Records are grouped into blocks, and each block stores a cryptographic hash of the previous block[1]
2. Changing an old record changes its hash, which invalidates every block after it, so the alteration is immediately detectable[1]
3. The ledger is copied across many computers, so a single altered copy disagrees with the rest and is rejecteddistribution is essential to the argument[1]
4. An ordinary database is better when one trusted organisation owns the data — it is far faster, cheaper and uses vastly less energy[1]

Chained hashes plus many copies make tampering detectable; a normal database is better when there is a trusted owner.

1. Records become accessible from any authorised device in the hospital, and from other sites if a patient is transferred[1]
2. The provider handles backup, redundancy and hardware maintenance, so the hospital needs no server room or specialist staff[1]
3. Risk: a loss of internet connectivity would make patient records unavailable, which in a hospital could be dangerous[1]
4. Risk: highly sensitive personal data is stored on a third party's hardware, possibly in another country with different privacy laws[1]
5. Measure: encrypt all records both in transit and at rest, so intercepted or stolen data is unreadable[1]
6. And keep a local cached or offline copy of critical records so care can continue during an outageaccept a contract specifying the country of storage[1]

(a) access anywhere, and no maintenance burden (b) outage risk and loss of control over sensitive data (c) encryption plus a local copy for outages

A legal issue concerns what the law permits — for example copying licensed software without paying, which breaches copyright. An ethical issue concerns what is right regardless of the law — for example a company legally selling users' browsing histories to advertisers without making that clear.

Phishing is an attempt to obtain personal information such as passwords by sending a message that imitates a trusted organisation. Recognise it by checking the sender's actual address and the real destination of any link, and by treating urgency — "your account will be closed today" — as a warning sign rather than a reason to hurry.

The digital divide is the gap between people who have reliable access to computers and the internet and those who do not — whether because of cost, location, or lack of skills. It matters because as services move online, those without access are excluded from them.

1. Collect only the data needed for a clearly stated purpose (data minimisation)[1]
2. Use it only for that stated purpose, and obtain informed consent[1]
3. Keep it accurate, secure and protected against unauthorised access[1]
4. Retain it no longer than necessary, and allow individuals to see and correct what is held about them[1]

Minimise, use only for the stated purpose, keep secure and accurate, and delete when done.

1. Ransomware is malware that encrypts the victim's files so they cannot be opened[1]
2. It then demands payment in exchange for the decryption key, with no guarantee the key will be supplied[1]
3. It encrypts everything it can reach, including attached backup drives and automatically synchronised cloud foldersthis is why ordinary backups fail[1]
4. A backup kept disconnected cannot be reached and therefore cannot be encrypted, so the files can be restored without paying[1]

It encrypts files and demands payment; only a disconnected backup is out of its reach.

1. It may well be legal, since the practice is disclosed in the terms the user agreed to[1]
2. But it is ethically questionable, because burying it in clause 47 of a document nobody reads means users have not meaningfully agreedboth categories must be addressed[1]
3. Informed consent requires the user to be told clearly, in plain language and before agreeing, exactly what is collected and who it is shared with[1]
4. It must be a genuine choice — the service should not be withheld unless the user agrees to data collection unrelated to providing it[1]
5. Harm: a continuous location history reveals home and workplace addresses, daily routines and religious or medical visits, enabling stalking or burglary[1]
6. Harm: it could be used for identity theft, blackmail, or discrimination by employers or insurersany second concrete harm[1]

(a) probably legal but ethically poor (b) plain language, in advance, a genuine choice (c) stalking or burglary from routine data; blackmail or discrimination

Quotation marks return only pages containing that exact phrase in that order. site: restricts results to a single domain, so site:gov.pk searches only Pakistani government pages.

Both are false. Misinformation is spread by someone who believes it is true; disinformation is spread deliberately, knowing it is false. The difference is intent.

The .org suffix is unrestricted — anyone may register one, including campaigning organisations and individuals with a case to argue. Unlike .edu and .gov, which are restricted, it carries no verification of any kind.

1. Author — is there a named author with relevant expertise, or is the page anonymous?[1]
2. Publisher — a university, government body or established organisation carries more weight than an unidentified site[1]
3. Date — on a fast-moving subject an old page may describe a situation that no longer exists[1]
4. Purpose and evidence — is it informing, selling or persuading, and does it cite sources that can be checked?[1]

Author, publisher, date, purpose and evidence — each with the reason it matters.

1. False claims are often written to be surprising or alarming, which makes people share them immediately[1]
2. A correction is careful and unexciting, arrives later, and reaches far fewer people than the original[1]
3. Action: verify before sharing — check the date, look for a second independent source, and read past the headline[1]
4. Action: notice your own emotional reaction, since content designed to make you angry is designed to be shared before it is checkedthe self-awareness point[1]

It is engineered to be shared while corrections are not. Verify before sharing, and be suspicious of your own strong reaction.

1. Look for the original source of the figure — an official energy authority, a government statistical release or an international agency[1]
2. Check the date, since energy figures change annually, and confirm what is being measured — installed capacity is not the same as electricity actually generatedthe capacity/generation distinction is the sharpest point here[1]
3. Seek a second independent source reporting a comparable figuresites repeating one original are not independent[1]
4. Cite the original authoritative source, not the website that repeated it, so the reader can verify the figure themselves[1]
5. Quoting reproduces the exact words, and requires quotation marks and a citation[1]
6. Paraphrasing restates the idea in your own words, and still requires a citation — the idea is not yours merely because the wording isthis is the point students most often get wrong[1]

(a) trace to the original, check date and what is measured, corroborate (b) the original source, so it can be verified (c) quoting needs marks and a citation; paraphrasing still needs the citation

Identifying a problem and building a business that solves it using digital tools and platforms — cloud services, online marketplaces, digital payments — rather than traditional premises and infrastructure. The entrepreneur takes the risk in exchange for the potential reward.

Freemium offers a basic version free and charges for an upgraded one. The risk is that free users still cost money to serve while only a small percentage ever upgrade, so the business can grow its user numbers and its losses at the same time.

The smallest version of a product that still delivers real value to a real user and generates feedback. Its purpose is to test the central assumption cheaply, before the full product is built.

1. An existing online marketplace or social media page provides an audience and a shopfront[1]
2. So there is no need to build a website or pay for premises before the first salethe explanation is the mark, not the naming[1]
3. A digital payment gateway accepts card and mobile paymentsaccept cloud hosting or free design tools[1]
4. So the seller can take money from anywhere without setting up merchant infrastructure of their own[1]

A marketplace supplies audience and shopfront; a payment gateway supplies the ability to take money.

1. Profit = revenue − costs = 400 000 − 350 000[1]
2. = Rs 50 000 per monththe business is profitable[1]
3. Money leaves the business immediately for wages but arrives 60 days later from customers[1]
4. So the account can be empty even though the business is profitable — this is a cash flow problem, and it can force closurenaming cash flow is expected[1]

Profit Rs 50 000/month, but a 60-day gap between paying costs and receiving revenue creates a cash flow problem.

1. Talk to farmers first to establish that identifying diseases is genuinely a problem they face and currently handle badlyvalidating the assumption[1]
2. Build an MVP where farmers send a photograph by WhatsApp and an agricultural expert replies manuallydelivers the value with no app[1]
3. Measure whether farmers use it repeatedly and whether they will pay, before writing any software[1]
4. A freemium or low-cost subscription model: a few free identifications, then a small monthly feeaccept any justified model[1]
5. Justified because the value is ongoing across a growing season, and farmers may be unwilling to pay before seeing it workthe justification must fit the customer[1]
6. Risks: farmers may have limited smartphone access or connectivity in rural areas; a wrong identification could destroy a crop and the business's reputationtwo risks needed[1]

(a) interview farmers, then run it manually over WhatsApp (b) freemium or low subscription, since value is ongoing (c) rural connectivity, and the consequences of a wrong diagnosis