Sonali, Janata Bank Officer (IT/ICT) Written Test: 2019 (AUST)প্রশ্ন ও সমাধান

Operations performed on a data structure

Operation	Purpose
Create	Reserve memory for a new data structure (compile-time or run-time, e.g. malloc())
Destroy	Free the memory occupied by a data structure (e.g. free())
Selection	Access a particular element within the structure
Update	Modify the value of an existing element
Search	Find whether a given item is present (and where)
Sort	Arrange all elements in a particular order (ascending/descending)
Merge	Combine two sorted lists into a single sorted list
Split	Partition one list into multiple lists
Traverse	Visit every node/element exactly once, in a systematic order

Prefix, Infix and Postfix notation

These describe where the operator sits relative to its operands in an expression:

graph LR
    A["Infix: A + B"] --> B["Prefix: + A B"]
    A --> C["Postfix: A B +"]

• Infix: operator is written between the two operands — the everyday form: A + B. Requires operator precedence/parentheses to remove ambiguity, which makes it harder for a machine to evaluate directly.
• Prefix (Polish Notation): operator is written before its operands: +AB. No parentheses ever needed; evaluated by scanning right to left, pushing operands and applying the operator to the top two when found.
• Postfix (Reverse Polish Notation): operator is written after its operands: AB+. Also parenthesis-free; evaluated by scanning left to right using a stack — this is what compilers actually convert expressions into internally, because it needs no precedence rules to evaluate.

Worked example: infix (A+B)*C → prefix *+ABC → postfix AB+C*.

Exam takeaway: infix is human-friendly but ambiguous without precedence rules; prefix/postfix remove that ambiguity entirely and are stack-evaluable in a single linear pass — which is exactly why compilers translate expressions to postfix before evaluating them.

Pulse Amplitude Modulation (PAM)

PAM is an analog pulse-modulation technique in which the amplitude of a train of regularly-spaced carrier pulses is varied in proportion to the instantaneous amplitude of the message (information) signal — the pulse positions and widths stay fixed; only their height changes. Demodulation recovers the message by detecting the amplitude level of each pulse.

graph LR
    M["Message signal<br/>(continuous analog)"] --> S["Sampler<br/>(samples at fixed intervals)"]
    S --> P["Pulse train whose<br/>AMPLITUDE follows the sample value"]
    P --> D["Demodulator<br/>(detects amplitude of each pulse)"]
    D --> O["Recovered message signal"]

Two sampling techniques are used: Flat-Top PAM (pulse amplitude held constant at the sampled value for the pulse duration — simpler to generate, mild distortion) and Natural PAM (pulse top follows the natural shape of the signal during sampling — more accurate, harder to generate).

Types of Computer Network

Networks are classified mainly by geographic span:

Type	Full form	Typical range	Example
PAN	Personal Area Network	A few metres	Bluetooth between phone and earbuds
LAN	Local Area Network	One building/campus	Office or home Wi-Fi network
MAN	Metropolitan Area Network	A city	Cable TV network across a city
WAN	Wide Area Network	Country/globe	The Internet itself

graph TD
    PAN[PAN - few metres] --> LAN[LAN - building/campus]
    LAN --> MAN[MAN - city]
    MAN --> WAN[WAN - country/world]

Exam takeaway: PAM encodes information purely in pulse amplitude (unlike PWM/PPM, which vary width/position); networks scale from PAN → LAN → MAN → WAN strictly by increasing geographic coverage, with the Internet being the ultimate WAN.