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

Case Manipulation Methods

• title(): Displays each word in a string in Title Case, where every word begins with a capital letter.
• upper(): Converts every character in a string to all uppercase letters.
• lower(): Converts every character in a string to all lowercase letters. This is particularly useful for normalizing user input before storing it.

Whitespace Stripping Methods

Python considers whitespace (tabs, spaces, etc.) significant. Use these methods to clean up extra spacing:

• rstrip(): Removes whitespace from the right side (end) of a string.
• lstrip(): Removes whitespace from the left side (beginning) of a string.
• strip(): Removes whitespace from both the beginning and the end of a string simultaneously.

Related Data Type Conversion

• str(): While not

In C++, Input/Output (I/O) operations are managed through a hierarchy of classes collectively known as streams. A stream is an abstraction that represents a flow of data between a source (like a keyboard) and a destination (like a screen).

Here is a comprehensive breakdown of how C++ handles both unformatted and formatted I/O operations, along with the core stream mechanisms.

Streams, Insertion, and Extraction

At the heart of C++ I/O are the standard stream objects:

• cin: Standard input stream (usually the keyboard), an instance of istream.
• cout: Standard output stream (usually the screen), an instance of ostream.

The Insertion Operator (<<)

Used with cout to output data. It "inserts" data into the output stream.

cout << "Hello, World!";

Single Inheritance in Java

This Single Inheritance program demonstrates how a child class inherits properties and methods from a single parent class.

class Animal {
    // Constructor of Parent class
    Animal() {
        System.out.println("Animal constructor called");
    }
    // Method of Parent class
    void eat() {
        System.out.println("I can eat");
    }
}

// Child class inheriting from Animal
class Dog extends Animal {
    // Constructor of Child class
    Dog() {
        System.out.println("Dog constructor called");
    }
    // Method of Child class
    void bark() {
        System.out.println("I can bark");
    }
}

// Main class to test inheritance
public class Main {
    public static void main(String[] args) {
        /

What is PHP?

PHP (Hypertext Preprocessor) is a widely-used open-source scripting language primarily designed for web development. It runs on the server-side, meaning the code is executed on the web server before the output is sent to the user's browser. PHP is embedded within HTML and supports various databases, making it a powerful tool for creating dynamic and interactive web applications.

Key Features of PHP

PHP has several features that make it a popular choice for web development:

• Open-Source – PHP is free to use, with a large community of developers providing support and updates.
• Cross-Platform Compatibility – PHP works on multiple operating systems like Windows, Linux, and macOS.
• Easy to Learn and Use – Its syntax is simple and similar

Bitcoin Consensus

The Problem: Decentralized Network

• Bitcoin operates without a central authority; all users must agree on transaction history.
• It faces the Byzantine Generals Problem; although unknown to each other, participants must establish trust.
• Trust is established using consensus protocols, incentives, and cryptography.

How It Works

• The Bitcoin algorithm operates on nodes.
• Any device (computer) running the full Bitcoin software and connected to the internet acts as a connection point for creating blocks and verifying transactions.
• When a block is created, nodes communicate to verify the transactions and ensure they follow the algorithm's rules.
• Each node maintains a complete copy of the Bitcoin blockchain.

Participants in the Ecosystem

• Full Nodes:

Arithmetic Mean

The following C++ code calculates the arithmetic mean of numbers from 1 to n:

int main() {
    int n;
    double suma = 0;
    cout << "Vnesi broj: ";
    cin >> n;
    if (n <= 0) {
        cout << "Brojot na elementi mora da bide pogolem od 0!" << endl;
        return 1;  
    }
    for (int i = 1; i <= n; i++) {
        suma += i;  
    }
    double sredina = suma / n;
    cout << "Aritmetichkata sredina na broevite od 1 do " << n << " e: " << sredina << endl;
    return 0;
}

Sum

The following C++ code calculates the sum of numbers from 1 to n:

int main() {
    int n, sum = 0;
    cout << "Vnesi broj n: ";
    cin >> n;
    for (int i = 1; i <= n; i++)

Understanding Variables & Data Types

Variables: Storing Data

Variables are containers used to store data. They are assigned values using the = operator (e.g., x = 5).

Essential Data Types

Python supports several fundamental data types:

• int: Represents integer numbers (e.g., 10, -5).
• float: Represents floating-point numbers (e.g., 3.14, -0.01).
• str: Represents strings of characters (e.g., "hello", "123").
• bool: Represents Boolean values, either True or False.

Type Casting: Converting Data Types

Type casting allows you to convert data from one type to another using functions like int(), float(), and str().

Example: x = int("5") converts the string "5" to an integer. y = float("3.14") converts the string "3.14" to a float.

Input and Output Operations

Getting

This program demonstrates the Banker's Algorithm, a classic deadlock avoidance strategy used in operating systems to manage resource allocation safely.

C Source Code

#include <stdio.h>

int n, m;
int alloc[10][10], max[10][10], need[10][10];
int avail[10], work[10], finish[10];

// Safety Algorithm
int checkSafety() {
    int seq[10], count = 0;

    for (int i = 0; i < n; i++) finish[i] = 0;
    for (int i = 0; i < m; i++) work[i] = avail[i];

    while (count < n) {
        int found = 0;
        for (int i = 0; i < n; i++) {
            if (!finish[i]) {
                int j;
                for (j = 0; j < m; j++) {
                    if (need[i][j] > work[j]) break;
                }
                if (j == m)

1) DIJKSTRA (SSSP) — STEP TABLE (PAST-PAPER INSTANCE A)

Given edges: a→b(2), a→c(7), a→e(10), b→d(2), c→d(1), c→g(2), d→f(2), e→g(1), f→g(2). Source = a.
Rule: Pick unsettled vertex with minimum dist; relax outgoing edges.

Vertices:   a   b   c   d   e   f   g

Init:
Dist      = 0   2   7   ∞  10   ∞   ∞
S = ∅

Step 1: Pick a (min=0), S={a}
Relax from a: already set b=2, c=7, e=10
Dist      = 0   2   7   ∞  10   ∞   ∞

Step 2: Pick b (min=2), S={a,b}
Relax b→d: dist(d) = dist(b)+2 = 2+2 = 4
Dist      = 0   2   7   4  10   ∞   ∞

Step 3: Pick d (min=4), S={a,b,d}
Relax d→f: dist(f) = 4+2 = 6
Dist      = 0   2   7   4  10   6   ∞

Step 4: Pick f (min=6), S={a,b,d,f}
Relax f→g: dist(g) = 6+2 = 8
Dist