Notes, summaries, assignments, exams, and problems for Computers

1. DES Structure

DES (Data Encryption Standard) is a symmetric key block cipher used for data encryption. It encrypts 64-bit plaintext using a 56-bit secret key.

DES uses a 16-round Feistel structure. The plaintext first undergoes initial permutation and is divided into left and right halves. In every round, the right half is processed using a round function and XORed with the left half. After 16 rounds, a final permutation is performed to generate the ciphertext.

Features

• 64-bit block size
• 56-bit key
• 16 rounds
• Uses Feistel structure

Advantages

• Simple implementation
• Efficient hardware encryption

Disadvantages

• Weak against brute-force attacks

2. AES Algorithm

AES (Advanced Encryption Standard) is a symmetric encryption algorithm used to secure digital communication.... Continue reading "Cryptography Fundamentals: DES, AES, RSA and Security" »

1. Armstrong Number Checker

Write a shell script to check whether a given number is an Armstrong number.

echo "Enter a number"
read c
x=$c
sum=0
while [ $x -gt 0 ]
do 
  r=$(( $x % 10 ))
  n=$(( $r * $r * $r ))
  sum=$(( $sum + $n ))
  x=$(( $x / 10 ))
done
if [ $sum -eq $c ]
then
  echo "This is an Armstrong number"
else 
  echo "This is not an Armstrong number"
fi

2. Calculate Area of a Circle

Write a shell script to find the area of a circle.

echo "Enter radius"
read r
echo "Area is"
echo "3.14 * $r * $r" | bc

3. Average of Command Line Arguments

Write a shell script to find the average of numbers entered as command line arguments.

sum=0
for i in $*
do
  sum=$((sum + i))
done
echo "Summation of $# numbers is: $sum"
N=$#
avg=$(echo "$sum / $N" | bc -l)
echo "Average = $avg"

Understanding Data Structures and Algorithms

8. Queues: FIFO Operations

A queue is a linear data structure that follows the First-In, First-Out (FIFO) principle. The element inserted first will be removed first, similar to people waiting in a line. It has two primary operations:

• enqueue(): Adds an element to the rear of the queue.
• dequeue(): Removes an element from the front of the queue.

Enqueue Operation Algorithm (Array-based):

1. Check if the queue is full (rear == size - 1).
2. If not full, increment rear.
3. Insert the new element at queue[rear].

Example:

if (rear == size - 1)
    printf("Queue Overflow");
else {
    rear++;
    queue[rear] = value;
}

Dequeue Operation Algorithm:

1. Check if the queue is empty (front > rear).
2. If not empty, retrieve the element

Experiment 5: Customer Analytics Database

This Python experiment demonstrates the practical application of core data structures: Tuples, Lists, Sets, and Dictionaries to build a basic Customer Analytics System.

# Experiment Code:
# Tuple: Fixed dataset structure (immutable)
dataset_schema = ("CustomerID", "Name", "PurchaseAmount", "Segment")
# List: Stores purchase amounts (mutable, ordered)
purchase_amounts = []
# Set: Stores unique customer IDs
unique_customers = set()
# Dictionary: Stores complete customer records
customer_records = {}

while True:
    print("\n--- Menu Customer Analytics ---")
    print("1. Add Customer Data")
    print("2. View Purchase Amounts (List)")
    print("3. View Dataset Schema (Tuple)")
    print("4. View Unique

Arithmetic Progressions (AP)

Sum of terms = n[(1st term + last term)]/2

Geometric Progressions (GP)

Sum of terms = [1st term(1 - quotientⁿ)/(1 - quotient)] (Swap positions of 1 & quotient if quotient > 1)

Logarithms

• log_a(x/y) = log_ax - log_ay
• log_axⁿ = nlog_ax
• log_ab = (log_cb/log_ca)

Permutations

For a set of n objects: The total number of permutations is n!

For arranging 'r' objects from a set of 'n' objects: The number of permutations is nPr = n! / (n-r)!. (e.g., ways to arrange 3 objects from a set of 5 is 5 * 4 * 3, since there are 5 possibilities for the first object, followed by 4, then 3.)

Combinations

For selecting 'r' objects from a set of 'n' objects: The number of combinations is nCr = n! / (r! * (n-r)!). (Divide by r! since there are r! ways

5G Enabling Technologies

5G is made possible by a combination of advanced radio, network, and computing technologies. These enabling technologies work together to deliver high data rates, ultra-low latency, massive connectivity, and high reliability.

1. Millimeter Wave (mmWave) Communication

5G uses high-frequency bands (typically 24 GHz–100 GHz) known as millimeter waves.

• Provides extremely high data rates
• Suitable for dense urban areas, stadiums, and hotspots
• Limited range, so it requires more base stations and small cells

2. Massive MIMO (Multiple Input Multiple Output)

Uses a large number of antennas at the base station.

• Increases spectral efficiency
• Supports multiple users simultaneously
• Improves data rates and coverage

3. Network Slicing

Divides... Continue reading "Core 5G Enabling Technologies and Sensor Network Architecture" »

In C++, Operator Overloading is a compile-time polymorphism feature that allows you to grant custom meanings to existing C++ operators (like +, -, *, ==, etc.) when they are applied to user-defined data types (objects).

It does not let you create new operators (you cannot invent a ** operator), nor does it change the precedence or associativity of existing ones. It simply makes your custom objects behave intuitively, like built-in data types.

1. Syntax of Operator Overloading

To overload an operator, you define a special member function using the operator keyword followed by the symbol you want to overload.

ReturnType operator Symbol (Arguments) {
    // Custom logic here
}

2. Overloading Unary Operators

A unary operator operates on a single operand.... Continue reading "Mastering C++ Operator Overloading: A Practical Tutorial" »

1. Arrays: Definition, Types, and Implementation

An array is a collection of elements of the same data type stored in contiguous memory locations. It is used to store multiple values in a single variable and can be accessed using index numbers. The indexing in an array starts from 0. Arrays help manage and process data efficiently, especially when dealing with large volumes of similar data.

Types of Arrays Based on Dimensions

• One-Dimensional Array: It stores data in a linear list format.
• Multi-Dimensional Array: It stores data in matrix form (like 2D, 3D arrays), which is useful in applications like image processing and tables.

Types of Arrays Based on Memory Allocation

1. Static Array:

   The size of the array is fixed at compile-time. Memory is allocated

Aggregation and Charting Commands

• Stats vs. Eventstats vs. Streamstats: stats collapses events for aggregation; eventstats retains events for per-event comparison; streamstats performs rolling, order-sensitive calculations.
• Chart vs. Timechart: Use chart for non-time data with over/by; use fillnull to handle gaps. timechart bins _time automatically; define intervals using span=12h. Note: chart count over X by Y differs from chart count by X,Y.

Data Manipulation and Filtering

• Eval: Use tostring(field, "duration") for numeric time formatting; case() for multi-condition logic; and coalesce(field1, field2, …) to prevent null values.
• Where vs. Search: where is a post-pipe, type-sensitive command. Strings treated as numbers result in nulls; cast using