WBBSE Madhyamik Computer Application (Optional) cheat sheet

A computer is an electronic device that accepts data (input), processes it under stored-program control, produces information (output) and may store results; IPO plus storage is the standard cycle.

Hardware generations: valves (1st), transistors (2nd), integrated circuits (3rd), VLSI microprocessors (4th); each generation reduced size, cost and power while raising speed and reliability.

Classification by size and power: supercomputer, mainframe, minicomputer, microcomputer; by data handled: analog, digital, hybrid.

Units: 1 nibble = 4 bits, 1 byte = 8 bits, 1 KB = 1024 B, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.

Positional number systems: binary (base 2, digits 0-1), octal (8, 0-7), decimal (10, 0-9), hexadecimal (16, 0-9 and A-F).

Place value of a digit = digit × base^position, positions counted from 0 at the right; the value of a numeral is the sum of these products.

Binary arithmetic rules: 0+0=0, 0+1=1, 1+1=10 (carry 1); 0×0=0, 1×1=1; subtraction borrows 2, not 10.

Binary to octal groups bits in threes from the right; binary to hexadecimal groups in fours; pad the leftmost group with zeros.

CPU parts: ALU performs arithmetic and logic, control unit fetches and decodes instructions and directs the flow, registers hold the current instruction, operands and addresses.

Primary memory is directly accessible to the CPU: RAM is volatile and read/write, ROM is non-volatile and holds firmware such as the bootstrap loader.

Cache memory sits between CPU and RAM; it is small, fast and expensive, and stores frequently used instructions and data to reduce access time.

Secondary storage is non-volatile: magnetic hard disk, optical CD/DVD, and solid-state pen drive or SSD; measured by capacity and access time.

Input devices: keyboard, mouse, scanner, microphone, joystick; output devices: monitor, printer, speaker, plotter.

System software includes the operating system, language translators (assembler, compiler, interpreter) and utility programs; application software serves a user task.

Compiler translates the whole program before execution and reports all errors together; interpreter translates and runs line by line and stops at the first error.

Operating system functions: process management, memory management, file management, device management and providing the user interface (CLI or GUI).

Decimal to any base: divide repeatedly by the target base, record remainders, and read remainders bottom to top.

Any base to decimal: multiply each digit by base^position (position 0 at the rightmost digit) and add the products.

Binary to decimal shortcut: assign weights 1, 2, 4, 8, 16, 32, 64, 128 from the right and add weights where the bit is 1.

Hexadecimal digits A-F stand for decimal 10-15; e.g. 2F₁₆ = 2×16 + 15 = 47₁₀.

Octal to binary: replace each octal digit by its 3-bit binary equivalent; binary to octal: regroup in threes from the right.

Hexadecimal to binary: replace each hex digit by its 4-bit binary equivalent (A = 1010, F = 1111).

Signed representation: sign-magnitude uses the leftmost bit as sign; 1's complement flips all bits; 2's complement = 1's complement + 1, and is the standard method for subtraction.

Character codes: ASCII uses 7 bits (128 codes), Extended ASCII 8 bits; ISCII and Unicode represent Indian and other scripts.

A byte can hold 2^8 = 256 distinct values; an n-bit register holds 2^n distinct patterns, ranging 0 to 2^n − 1 unsigned.

Algorithm properties: finite (terminates), definite (each step unambiguous), effective, and has zero or more inputs and one or more outputs.

Flowchart symbols: oval = start/stop, parallelogram = input/output, rectangle = process, diamond = decision, arrow = flow line, circle = connector.

Decision (diamond) has one entry and two exits, labelled Yes/No or True/False; only one path is followed.

Sequence, selection and iteration are the three basic control structures; every algorithm can be built from them.

Swapping two variables needs a third temporary variable: temp = a; a = b; b = temp.

Sum of first n natural numbers: n(n+1)/2; this replaces a loop and is a standard algorithm-efficiency example.

To find the largest of three numbers, compare pairs and keep a running maximum; each comparison is a decision step.

Dry run (trace table) executes the algorithm step by step on sample data, recording variable values to verify correctness.

Identifier rules: begins with a letter or underscore, contains letters, digits or underscore, no spaces or special symbols, not a reserved keyword, case-sensitive.

Data types: int (whole numbers), float (real numbers), char (single character in single quotes), string (character sequence), boolean (true/false).

Arithmetic operators: + − * / with integer division discarding the fractional part and % (modulus) giving the remainder; both operands must be integers for % and integer division.

Relational operators: ==, !=, <, >, <=, >= return true or false; = is assignment, == is comparison.

Logical operators AND, OR, NOT combine conditions; AND is true only when both operands are true, OR is false only when both are false.

Operator precedence: parentheses first, then unary, then * / %, then + −, then relational, then logical NOT/AND/OR; assignment last.

if-else selects one of two blocks; else-if ladder or switch handles multiple exclusive cases; the condition of if must be a boolean expression.

Loops: for (known count), while (test before body), do-while (body executes at least once); every loop needs an initialisation, a condition and an update.

break exits the nearest loop or switch immediately; continue skips the rest of the current iteration and proceeds to the next test.

An array is a collection of elements of the same data type stored in contiguous memory and accessed by a single name plus an index.

In most languages (C, Java) array indexing starts at 0, so an array of n elements has valid indices 0 to n−1; accessing index n is an out-of-bounds error.

Traversing an array requires a loop from the first index to the last; the loop counter doubles as the index.

Linear search checks elements one by one and works on unsorted data; binary search requires sorted data and repeatedly halves the search range.

Bubble sort compares adjacent pairs and swaps them when out of order; after k passes the k largest elements are in final position.

A string is an array of characters terminated by a null character in C; the length excludes the terminator.

Common string operations: length, concatenation, comparison, substring extraction, and case conversion; comparison is character by character using character codes.

2-D array element is addressed by two indices, row and column; total elements = rows × columns, and nested loops are used for traversal.

Network types by span: PAN (personal, few metres), LAN (building/campus), MAN (city), WAN (countries/global).

Topologies: bus (single backbone, cheap, one break halts all), star (central hub, easy fault isolation), ring (closed loop, data in one direction), mesh (every node linked, most reliable, costly).

Transmission media: guided - twisted pair, coaxial cable, optical fibre (highest bandwidth, immune to EMI); unguided - radio, microwave, satellite.

Bandwidth is the data-carrying capacity of a channel; a protocol is a set of rules governing data exchange (TCP/IP is the Internet suite).

IP address identifies a device on a network; DNS translates human-readable domain names into IP addresses.

URL parts: protocol (http/https), domain name, path and resource; HTTP transfers web pages, SMTP sends mail, FTP transfers files.

The Internet is a global network of networks; the World Wide Web is a service on it accessed through browsers using hyperlinks.

Network devices: hub broadcasts to all ports, switch forwards by MAC address, router forwards packets between networks by IP address, modem converts digital and analog signals.

Malware families: virus (attaches to files), worm (self-replicates across networks), Trojan (disguised as useful software), spyware (secretly collects data), ransomware (encrypts data for payment).

Phishing is a fraudulent message that imitates a trusted source to steal credentials; check the sender address and never enter passwords via links in mail.

Strong password practice: long, mixed case, digits and symbols, unique per site, changed after any suspected breach; never share it or store it in plain text.

Firewall filters incoming and outgoing traffic by rules; antivirus detects known malware signatures and should be updated regularly.

Digital footprint is the permanent trace of online activity; posts, images and comments may persist and be copied even after deletion.

Cyber ethics: do not access others' accounts or data without permission, do not plagiarise, respect copyright and software licences, no cyberbullying or hate content.

Personal data protection: avoid sharing address, phone number, school name or live location publicly; use privacy settings and verify before posting.

Indian legal context: the Information Technology Act, 2000 addresses cyber offences such as identity theft, publishing obscene material and unauthorised access.

Report cybercrime through the national cybercrime reporting portal or the local police cyber cell; preserve screenshots and logs as evidence.

E-governance uses ICT for citizen services: online certificates, land records, digital payments and grievance portals.

E-commerce models: B2B (business to business), B2C (business to consumer), C2C (consumer to consumer); online payment uses UPI, cards or net banking.

Cloud computing delivers computing resources (storage, servers, software) over the Internet on demand; service models are IaaS, PaaS and SaaS.

Artificial intelligence builds systems that perform tasks needing human-like intelligence: pattern recognition, decision-making, natural language processing.

Machine learning trains models on data to make predictions rather than following hand-written rules; more representative data improves accuracy.

IoT (Internet of Things) connects everyday physical devices with sensors and network links to collect and exchange data, e.g. smart meters and health wearables.

Blockchain is a distributed, append-only ledger of cryptographically linked blocks; it underlies cryptocurrency and tamper-evident record keeping.

Big data refers to very large, fast and varied datasets analysed for patterns; education, health, agriculture and banking are major application areas.

Social media and digital India initiatives illustrate computing applications in communication, financial inclusion and public service delivery.

Practical record structure: aim, requirements (hardware/software), procedure or algorithm, program listing, sample input with expected and observed output, conclusion.

Before writing code, prepare the algorithm and flowchart; the program listing must match the logic shown in them.

Compile and run the program with at least three test cases: normal data, boundary values and invalid input; record actual output.

Debugging method: read the error message, locate the line, check variable values by printing them, fix one error at a time and re-run.

Common syntax errors: missing semicolon, unmatched braces or parentheses, wrong case in keywords, undeclared variable, wrong format specifier.

Common logic errors: off-by-one loop bounds, using = instead of ==, uninitialised variables, wrong array index range.

Lab safety and care: shut down properly, keep magnetic media away from magnets, do not delete system files, save work frequently.

Project documentation should state the problem, inputs, processing logic, output format and limitations, with screenshots of the running program.