Tamil Nadu HSE Second Year Computer Applications cheat sheet

Data units scale by 1024: 8 bits = 1 byte (B), 1 KB = 1024 B, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.

Number system bases: binary 2 (digits 0-1), octal 8 (0-7), decimal 10 (0-9), hexadecimal 16 (0-9, A-F where A=10 ... F=15).

Binary to decimal: multiply each bit by 2 raised to its position from the right, starting at 2^0; e.g. 1011 = 8+0+2+1 = 11.

Decimal to binary: repeatedly divide by 2 and read remainders bottom-to-top; 25 gives 11001.

Grouping rule: 3 binary bits = 1 octal digit; 4 binary bits = 1 hexadecimal digit, so conversion between binary, octal and hex is by grouping only.

1's complement flips every bit; 2's complement = 1's complement + 1 and represents negatives, so an n-bit signed range is -2^(n-1) to 2^(n-1) - 1.

Character codes: ASCII uses 7 bits (0-127); extended ASCII uses 8 bits; Unicode (UTF-8/UTF-16) covers all world scripts.

Logic gates: AND gives 1 only if all inputs are 1; OR gives 1 if any input is 1; NOT inverts; NAND and NOR are the negations of AND and OR.

Generations: first used vacuum tubes, second transistors, third integrated circuits, fourth microprocessors, fifth AI and parallel processing.

Von Neumann architecture: input unit, memory unit, arithmetic logic unit, control unit and output unit, with instructions and data stored in the same memory.

CPU parts: ALU performs arithmetic and logic; control unit fetches, decodes and directs execution; registers hold the current instruction, address and operands.

Memory hierarchy from fastest and smallest to slowest and largest: registers, cache, main memory (RAM), secondary storage (SSD/HDD), offline backup.

RAM is volatile and holds running programs; ROM is non-volatile and stores firmware such as BIOS; cache sits between CPU and RAM.

Primary vs secondary memory: primary is directly addressed by the CPU, secondary is accessed via I/O and retains data when power is off.

OS functions: process management, memory management, file system management, device management, security and user interface.

Types of OS: batch, multiprogramming, multitasking, time-sharing, real-time (hard/soft) and distributed.

A process state moves through new, ready, running, waiting and terminated; the scheduler picks the next ready process.

Utility and language software: assembler translates assembly to machine code, compiler translates the whole source at once, interpreter translates line by line.

Word processor file formats: .docx (default Word), .odt (OpenDocument), .rtf (rich text interchange), .txt (plain text, loses formatting), .pdf (fixed layout).

Editing shortcuts: Ctrl+C copy, Ctrl+X cut, Ctrl+V paste, Ctrl+Z undo, Ctrl+Y redo, Ctrl+A select all, Ctrl+F find, Ctrl+H replace.

Formatting shortcuts: Ctrl+B bold, Ctrl+I italic, Ctrl+U underline, Ctrl+E centre, Ctrl+L left align, Ctrl+R right align, Ctrl+J justify.

Font size is measured in points (1 point = 1/72 inch); line spacing options include single, 1.5 and double.

Header appears at the top and footer at the bottom of every page; page numbers are inserted as a field inside the header or footer.

Mail merge combines a main document with a data source (table of records) to produce one personalised copy per record.

Tables are built from rows and columns; cells can be merged or split, and borders/shading are table properties, not paragraph properties.

Track changes records insertions and deletions for review; comments attach notes without altering the text.

Print settings include page range, orientation (portrait/landscape), paper size, margins and copies.

A cell reference combines column letter and row number (B7); a range is written A1:C10; the active cell is shown in the name box.

Relative reference (A1) shifts when copied; absolute reference ($A$1) stays fixed; mixed ($A1 or A$1) fixes only the column or only the row.

Formula entry always begins with = (or + or -); arithmetic operators are + - * / ^ and comparison operators return TRUE or FALSE.

Common functions: =SUM(A1:A5), =AVERAGE(A1:A5), =MAX(), =MIN(), =COUNT() (numbers only), =COUNTA() (non-empty cells), =IF(condition, value_if_true, value_if_false).

Error values: #DIV/0! divide by zero, #VALUE! wrong data type, #REF! deleted reference, #NAME? unrecognised function name, ##### column too narrow.

Sorting arranges rows by one or more keys; filtering hides rows that fail a condition without deleting them.

Charts: column/bar compare categories, line shows trend over time, pie shows parts of a whole (one data series only), scatter shows correlation.

In a slide show, slide transition is the effect between slides, while animation applies to individual objects on one slide.

Presentation views: Normal for editing, Slide Sorter for reordering, Slide Show (F5) for delivery; Ctrl+M inserts a new slide.

An algorithm is a finite, ordered, unambiguous set of steps; a flowchart draws it with oval (start/end), parallelogram (input/output), rectangle (process), diamond (decision) and arrow (flow).

Program development cycle: problem definition, algorithm/flowchart design, coding, compilation or interpretation, testing and debugging, documentation.

C++ structure: #include directives, using namespace std;, int main() with a return 0; statement, braces delimiting blocks, semicolon ending each statement.

C++ data types: int (whole numbers), float/double (real), char (single character), bool (true/false), void (no value); sizeof gives size in bytes.

Python is interpreted and dynamically typed; variables need no declaration, indentation defines blocks, and the type is inferred at assignment.

Python input() always returns a string, so numeric input needs int(input()) or float(input()); print() separates arguments with a space by default.

Operators: + - * / % (modulus, remainder) and // (floor division in Python); == is comparison, = is assignment.

Operator precedence: parentheses first, then exponent, then * / % //, then + -, then comparison, then logical not/and/or.

Comments: // single line and /* ... */ multi-line in C++; # in Python. Comments are ignored by the compiler/interpreter.

Sequence, selection and iteration are the three control constructs; any algorithm can be written using only these.

Selection: if, if-else, else-if ladder, nested if; the switch statement compares one expression against constant case labels and needs break to avoid fall-through.

Iteration: while tests before the body, do-while tests after the body (runs at least once), for combines initialisation, condition and update in one line.

Loop control: break exits the nearest loop immediately; continue skips the rest of the current iteration and re-tests the condition.

A function header gives return type, name and parameter list; a value-returning function uses return, a void function returns nothing.

Call by value passes a copy (changes are local); call by reference (C++ & parameter) lets the function modify the original variable.

Scope: a local variable exists only inside its block; a global variable is declared outside all functions and is visible throughout the file.

An array stores a fixed number of same-type elements in contiguous memory; indices run 0 to n-1, so accessing index n is out of bounds.

A 2-D array is declared as type name[rows][cols] in C++ and accessed as a[i][j]; Python lists use a[i][j] with zero-based indexing.

Recursion is a function calling itself and must have a base case that stops the calls, or it causes stack overflow.

A relation is a table, a tuple is a row, an attribute is a column; the degree is the number of columns and the cardinality is the number of rows.

Keys: primary key uniquely identifies each row and cannot be NULL; candidate keys are alternatives; foreign key references another table's primary key and enforces referential integrity.

DDL commands define structure: CREATE, ALTER, DROP, TRUNCATE. DML commands handle data: SELECT, INSERT, UPDATE, DELETE.

SELECT syntax order: SELECT columns FROM table WHERE condition GROUP BY column HAVING condition ORDER BY column [ASC|DESC];

WHERE filters individual rows before grouping; HAVING filters groups after GROUP BY and is used with aggregate functions.

Aggregate functions: COUNT(), SUM(), AVG(), MIN(), MAX(); they ignore NULL except COUNT().

Operators in WHERE: = <> > < >= <=, BETWEEN a AND b, IN (list), LIKE with % (any string) and _ (one character), IS NULL, AND/OR/NOT.

Joins: INNER JOIN returns matching rows only; LEFT/RIGHT OUTER JOIN keeps unmatched rows from one side with NULLs; CROSS JOIN is the Cartesian product.

DISTINCT removes duplicate rows; DELETE removes rows but keeps the table, DROP removes the table entirely.

Network by size: PAN (personal, ~10 m), LAN (building/campus), MAN (city), WAN (country/global); the Internet is the largest WAN.

Topologies: bus (single backbone, cheap, one break kills the line), star (central hub/switch, easy fault isolation), ring (token passing), mesh (every node linked, most reliable, most cabling).

Transmission media: twisted pair (Ethernet), coaxial, fibre optic (light, high bandwidth, immune to EMI), plus wireless radio, microwave and satellite.

OSI has 7 layers (Physical, Data Link, Network, Transport, Session, Presentation, Application); TCP/IP has 4; each layer serves the one above it.

Protocols: IP addresses and routes packets, TCP is connection-oriented and reliable, UDP is connectionless, HTTP/HTTPS for web, FTP for files, SMTP for sending mail, POP3/IMAP for receiving.

IPv4 is a 32-bit address in four dotted octets (0-255); IPv6 is 128-bit written in hexadecimal.

DNS maps domain names to IP addresses; a URL has scheme, host/domain, path and file, e.g. https://www.example.com/page.html.

Web terms: browser is the client, web server hosts pages, HTTP is stateless, a cookie stores small client-side state, a search engine indexes pages.

Bandwidth is capacity in bits per second; latency is delay; a switch forwards within a LAN by MAC address, a router forwards between networks by IP address.

HTML document skeleton: , , (metadata, , <meta>, <link>) and <body> (visible content).</p>

Text tags:

paragraph,
line break (empty tag),

Lists:

unordered (bullet),
ordered (numbered, with type and start attributes), definition list with and .

Links and media: for hyperlinks (target="_blank" opens a new tab), for images (empty tag),

Forms:

Semantic tags:

CSS rules: selector { property: value; } and can be inline (style attribute), internal (

Selectors: element (p), class (.note), id (#main), descendant (div p); id must be unique in a page, a class can repeat.

Box model from inside out: content, padding, border, margin; box-sizing: border-box makes width include padding and border.

CSS properties: color (text), background-color, font-family, font-size, text-align, display (block, inline, inline-block, none).

Cloud service models: IaaS supplies virtual machines and storage, PaaS supplies a development platform, SaaS supplies ready applications; deployment types are public, private and hybrid.

Cloud benefits are on-demand self-service, broad network access, resource pooling, elasticity and measured pay-per-use billing.

IoT is a network of physical devices with sensors and actuators exchanging data; its layers are perception (devices), network (transport) and application.

AI subfields: machine learning (learns from data), natural language processing (text and speech), computer vision (images), robotics and expert systems.

E-commerce models: B2B (business to business), B2C (business to consumer), C2C (consumer to consumer via marketplaces), plus m-commerce on mobile devices.

E-commerce payment and security: payment gateways encrypt card data, digital signatures verify authenticity, and HTTPS with SSL/TLS protects data in transit.

Malware types: virus attaches to files, worm spreads itself over networks, trojan hides inside useful software, ransomware encrypts data and demands payment, spyware secretly collects data.

Phishing is a fake message that lures credentials; pharming redirects to a fake site via DNS; keyloggers record keystrokes; firewalls filter traffic by rules.

Safe practice rules: use strong unique passwords with two-factor authentication, keep software patched, avoid unknown links and downloads, back up data, and never share OTPs or passwords.