Notes, summaries, assignments, exams, and problems for Computer science

How the World Wide Web Works

The World Wide Web is the most widely used part of the internet. When you browse the web, you view multimedia pages containing text, pictures, graphics, sounds, and videos. The web uses hypertext links to allow you to navigate from one place to another.

The web operates on a client/server model: client software (the web browser) runs on your computer, while server software runs on a web host.

To use the web, you need an internet connection and a web browser. You type the URL for the website you wish to visit, and your browser sends a request using the HTTP protocol. This is how the browser and server communicate. When the server finds the requested page, it sends it back to the browser.

How Web Pages Are Organized

The...

1. Login

Enter your provided username and password to access the application.

2. Tony’s Introduction

Click the Play button to watch the introductory video. To proceed, select Start Using the App.

3. Plans Page

This page displays your created financial plans. If you are a first-time user, you will see a single button; click the icon to create your first plan. If you have existing plans, use the following options:

• Create a new plan
• Clone an existing plan
• Delete an existing plan

4. Summary Page

View a comprehensive summary of your income, anticipated income, income tax, and both liquid and illiquid assets.

5. Navigation Menu

represents the Menu button. Clicking this icon opens a slider menu, which is accessible from every page within the application....

C Example 1: Writing Structured Data to a File

This program demonstrates appending structured date data (assuming struct fecha is defined elsewhere) to a file named Dades.txt. It includes basic file opening and error checking.

#include <stdio.h>
#include <stdlib.h>

int main() 
{
    int temp = 1;
    int auxiliar = 0;
    int i = 0;
    FILE *v1;
    
    v1 = fopen("Dades.txt", "a");
    
    // Note: Variables 'origen' and 'destino' are undefined in this snippet.
    if (origen == NULL || destino == NULL) {
        printf("Problemas con los ficheros.\n");
        exit(1);
    }
    
    printf("Inserte el día, mes y año. El programa finalizará marcando 0 en el día:\n\n");
    
    while (temp != 0) {
        printf("Día:\

Welcome to Chops 6

This new version of Chops is full of exciting new features. Want to take a look?

New interface

Chops now has a more consistent, fast, and attractive interface. Also, the program windows are dockable, and you can customize the program in many different ways. Try the Options tab and the Window Layout button.

Edit several documents at once

Another key development in Chops is the ability to work with several documents at once. Now you can create a summary of a document in the same window or compare differences between two texts, for example. Try opening a new blank document and clicking the Options tab, or drag the open document tab to rearrange the desktop layout.

Live preview and contextual tabs

Try clicking the picture accompanying...

Software Validation and Verification Fundamentals

Objectives of Validation and Verification

• Detect and correct defects as soon as possible.
• Reduce risks of budget and timetable deviations.
• Improve software quality and reliability.
• Improve development process management visibility.
• Quickly assess proposed changes.

Philosophy of Software Testing

Recommendations by G.J. Myers:

• Each test case should define the expected output.
• Programmers must avoid testing their own programs.
• Thoroughly inspect test results to identify possible symptoms of defects.
• Test case generation should include valid, invalid, and unexpected inputs.
• Prove that the software performs as intended and avoids unintended actions.
• Test plans should always assume the presence of defects to avoid

1. Functions of the File System

File systems structure information stored in a storage unit (typically a hard disk), which is then represented textually or graphically using a file manager. Most operating systems manage their own file system.

2. Operating System Responsibilities

The operating system performs several critical tasks, including:

• Sending commands to hardware devices.
• Detecting and managing system interrupts.
• Monitoring and checking for errors.

3. Understanding File System Architecture

A hard drive consists of several circular disks rotating around an axis. The tracks (concentric areas written on both sides of the disc) are divided into segments called sectors, each containing 512 bytes.

4. Definition of a Computer File

A file is a set of...

Information Technology and Communication (ICT)

Technologies based on microelectronics, robotics, computer, and communication networks.

Computing Fundamentals

Computing: The set of techniques and activities that address information, allowing it to be stored quickly and automatically with computers.

System: The set of elements needed to perform automatic processing of information.

Hardware Components

Hardware: Includes all the physical elements of the computer system.

Computer: A machine that can automatically receive information, store it in memory, and process it using programs or instruction sets.

Microprocessor (CPU): Responsible for coordinating and carrying out all operations of the system.

Peripherals

External elements that allow communication between...

Backup

Important directories: /etc, /home, /var, /usr, /local

Package and compress with tar. Files: home.tar

# tar -cvf home.tar /home

Compression:

# gzip -r /home/* (recursive compression)

Decompression:

# gunzip -r /home/* (recursive decompression)

Cryptography

In cryptography, digital signatures are a digital information authentication method, known as signature.

The art of cryptanalysis is the study of attempts to break ciphertext.

Key + algorithm + message = ciphertext

CID + Authentication + Irretrievability

Encryption: C = Ek(M). Decryption: M = Dk(C)

Steganography: secret communication by hiding the existence of the message.

Steganalysis: detection of steganographic content.

Examples of cryptographic protocols: SSL, SSH, IPSec, WEP, WPA

Symmetric algorithms:...

Network Routing and Switching

Switching: The process of moving packets from a router's input to the appropriate router output.

Routing: The process of determining the specific route taken by packets across a network.

Ethernet Frames and IP Datagrams

Ethernet frames: These typically have a Maximum Transmission Unit (MTU) of 1500 bytes.

IP Datagram: Key components include the identification flag (where the last fragment has the bit set to zero) and travel/offset (which specifies the exact location of the fragment).

Address Resolution Protocol (ARP)

ARP: IP ARP is used to determine the physical address (MAC) of the next hop. It sends ARP requests for the destination MAC in broadcast mode, receives the response in unicast mode, and then forwards the packet...