C-DAC C-CAT cheat sheet

Subject-verb agreement: a singular subject takes a singular verb even when a plural noun sits inside a prepositional phrase ("The list of items is long"); compound subjects joined by "and" take a plural verb unless they form one idea.

Neither/either/each/every/everyone/none as subject pronouns are grammatically singular: "Neither of the answers is correct"; "none" may take a plural verb only when it clearly means "not any of them".

Tense sequencing: past perfect (had + past participle) marks the earlier of two past actions; present perfect (has/have + participle) links a past action to the present and rejects a definite past time marker such as "yesterday".

Conditionals: Type 1 if + present, will + base; Type 2 if + past simple, would + base; Type 3 if + past perfect, would have + participle. Mixed conditionals mix a past condition with a present result.

Active-to-passive conversion moves the object to subject position and uses be + past participle in the same tense: "They wrote the report" becomes "The report was written (by them)".

Common confusables tested: affect (verb) vs effect (noun), principal (main/head) vs principle (rule), complement (completes) vs compliment (praise), stationary (fixed) vs stationery (paper goods).

Reading comprehension strategy: answer only from the passage; the correct option paraphrases the text, while distractors reuse exact words from the passage but reverse or overstate the meaning.

Antonym/synonym items are best solved by placing each option in a sentence frame; a word that fits the frame but shifts register (formal vs colloquial) is usually the wrong choice.

Series rule check order: differences, then second differences, then ratios, then alternating sub-series (odd positions and even positions follow separate rules).

Alphabet positions: A=1 to Z=26; reverse value = 27 minus forward value. Opposite (A-Z, B-Y) pairs sum to 27, useful for letter-shift coding.

Coding-decoding: test a fixed shift first, then reversal of the word, then position-based codes (letter number, sum of letters, first-last swapping) before assuming a complex rule.

Blood relations: draw a family tree with gender symbols and generations as rows; "brother of my father" is uncle, "son of my sister" is nephew, "daughter of my mother's brother" is cousin.

Direction sense: fix north up; a left turn after facing north means west, and a right turn after facing south means west. Net displacement uses Pythagoras when the path is not a straight line.

Syllogism: only the conclusion that holds in every possible Venn arrangement of the premises is valid; "some A are B" does not imply "some B are not A", and "all A are B" does not imply "all B are A".

Seating arrangement: for linear rows, "A is third to the left of B" fixes relative position only; anchor the arrangement with one absolute clue (an end seat or a named center seat) before filling others.

Non-verbal series: track four attributes separately - number of sides, rotation direction and angle, shading/line fill, and element addition or removal. Each usually follows an independent rule.

Odd-one-out in figures: compare symmetry, number of enclosed regions, line intersections, and whether the figure can be drawn without lifting the pen (Euler path: 0 or 2 odd-degree vertices).

Percentage change: successive changes of a% then b% give a net change of a + b + ab/100 percent; a 20% rise followed by a 20% fall is a net 4% fall.

Profit and loss: profit% = (SP − CP)/CP × 100, always on cost price unless stated; two articles sold at the same price with equal gain% and loss% always yield a net loss of (x²/100)%.

Simple interest SI = PRT/100; compound interest CI = P(1 + R/100)^T − P. For 2 years the gap between CI and SI is P(R/100)².

Time-speed-distance: convert km/h to m/s by multiplying by 5/18. A train of length L crossing a platform of length P at speed v takes (L + P)/v.

Boats and streams: downstream speed = boat + stream, upstream = boat − stream; boat speed = (down + up)/2, stream speed = (down − up)/2.

Ratio and mixture: alligation gives the ratio of two components as (mean − cheaper) : (dearer − mean); repeated dilution of a container by replacing k litres n times leaves original × (1 − k/V)^n.

Permutation and combination: arrangements of n distinct items = n!; selections = nCr = n!/(r!(n−r)!); circular arrangements of n distinct items = (n−1)!.

Mensuration: circle area πr², circumference 2πr; cylinder volume πr²h, curved surface 2πrh; cone volume (1/3)πr²h, curved surface πrl with l = √(r² + h²); sphere volume (4/3)πr³.

Work and time: if A alone takes a days and B alone b days, together they take ab/(a + b) days; efficiency is inversely proportional to time taken.

Number systems: binary 1011 = 11 decimal; hexadecimal digits A-F = 10-15. Convert decimal to binary by repeated division by 2 reading remainders upward; group 4 bits to get one hex digit.

Two's complement: to negate a binary number, invert all bits and add 1. An n-bit signed range is −2^(n−1) to 2^(n−1) − 1, so 8-bit signed covers −128 to 127.

Logic gates: AND outputs 1 only if all inputs are 1; OR outputs 1 if any input is 1; XOR outputs 1 when inputs differ; NAND and NOR are universal gates.

Memory hierarchy from fastest and smallest to slowest and largest: registers, cache (L1/L2/L3), main memory (RAM), then secondary storage (SSD/HDD). RAM is volatile; ROM is non-volatile.

1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB. A byte is 8 bits; one hex digit encodes 4 bits, so 2 hex digits encode one byte.

C operators: integer division truncates (7/2 = 3), % gives remainder, ++x increments before use while x++ uses the value then increments; && and || short-circuit, so the right operand may never be evaluated.

C control flow: a for loop runs its condition before each iteration and its update after each iteration; while checks first (may run zero times); do-while runs at least once.

Arrays and strings in C are zero-indexed; a string is a char array terminated by the null character '\0', so "cat" needs 4 bytes of storage.

OS and networking basics: an operating system manages processes, memory and files; the CPU executes the fetch-decode-execute cycle; IPv4 addresses are 32 bits and IPv6 addresses are 128 bits.