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

Internet vs. World Wide Web (WWW)

• Internet: A global network infrastructure that uses TCP/IP to connect devices worldwide.
• WWW (World Wide Web): A multimedia service built upon the Internet, utilizing HTML, CSS, web browsers, and hyperlinks.
• Webpage: A single document accessible via the WWW. | Website: A collection or group of related webpages.

History and Evolution of the Internet

• 1960s: Development of ARPANET (Advanced Research Projects Agency Network).
• 1983: Adoption of the TCP/IP protocol suite (developed by Vint Cerf and Bob Kahn).
• 1989: Invention of the World Wide Web (WWW) by Tim Berners-Lee.
• 1992: Release of the Mosaic browser (developed at UIUC), popularizing the graphical web.

Understanding the Client-Server Model

• Client: Initiates a request

1. Modern Validation APIs (Constraint Validation API)

For advanced tracking and custom error messaging, JavaScript provides the Constraint Validation API. This API gives you deep programmatic control over HTML5 validation states.

Key Properties & Methods

• element.validity: An object containing boolean properties describing the validity state of the input.
  • validity.valueMissing: True if required but empty.
  • validity.typeMismatch: True if the syntax doesn't match the type (e.g., an invalid email).
  • validity.tooShort: True if it doesn't meet minlength.
  • validity.valid: True if the element passes all validation checks.
• element.setCustomValidity(string): Sets a custom error message. If you pass an empty string "", the field becomes valid again.
• element.checkValidity(

Web Security Fundamentals

Common Cross-Site Scripting (XSS) Types

Ejercicio de descuentos:

#!/bin/bash

read -p "¿Desea el billete también de vuelta? (s/n): " idavuelta

until [ $idavuelta=="s" ] || [ $idavuelta=="n" ]; do

read -p "¿Desea el billete también de vuelta? (s/n): " idavuelta

done

read -p "¿Tiene carnet joven? (s/n): " carnetjoven

until [ $carnetjoven="s" ] || [ $carnetjoven="n" ]; do

read -p "¿Tiene carnet joven? (s/n): " carnetjoven

done

descuento=0 billete=20

if [ $idavuelta="s" ]; then

descuento=20

billete=" expr $billete \* 2'

fi

if [ $carnetjoven="s" ]j then

descuento=30

fi

costefinal=`expr $billete \* \( 100 - $descuento \) / 100`

echo "El precio final del billete es $costefinal"

Ejercicio de medias:

#!/bin/bash

acu=0

cont=0

read -p "Introduce un numero: " num

while [ $num -ne 0 ]; do

acu=`expr $acu + $num`

cont=... Continue reading "Shell script" »

Universal Data Science Python Template

This template provides a streamlined workflow for common data science tasks, including data preprocessing, modeling, and visualization.

Step 1: Import Libraries

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns
from sklearn.model_selection import train_test_split
from sklearn.preprocessing import StandardScaler
from sklearn.linear_model import LogisticRegression, LinearRegression
from sklearn.cluster import KMeans, DBSCAN
from sklearn.metrics import accuracy_score, r2_score, silhouette_score

Step 2: Load Dataset

df = pd.read_csv('your_dataset.csv') # Replace with your dataset name
print(df.head())

Step 3: Data Cleaning

df = df.dropna()

Step 4: Feature Selection

X = df.drop(

Jose Andres Gutierrez Vargas

Email: [email protected]
Phone: [Your Phone Number]

Professional Summary

Results-driven and highly motivated Software Developer with extensive expertise in backend and frontend development, RESTful APIs, and database management. Skilled in SQL and NoSQL databases, with in-depth experience in Node.js for building scalable and high-performance applications. Adept at optimizing system performance, troubleshooting technical issues, and implementing innovative solutions.

Former Frontend Developer at Google, where I contributed to the development of dynamic and interactive web applications, enhancing user experiences through cutting-edge technologies. Passionate about software development, staying updated with the latest... Continue reading "Jose Andres Gutierrez Vargas: Software Developer Profile" »

Problem Statement 16: Coin Change

Given a set of coins and a value, find the minimum number of coins to satisfy the given value.

Test Case 1:

Coins: {25, 20, 10, 5}, Value: 50 cents

Used coin: 25 cents

Used coin: 25 cents

Total number of coins: 2

Test Case 2:

Coins: {25, 20, 10, 5}, Value: 73 cents

Used coin: 25 cents

Used coin: 25 cents

Used coin: 20 cents

Used coin: 3 cents

Total number of coins: 4

Code:

-
#include int main { int amount =
50; int coins[] = {25, 20, 10, 5}; int
numCoins = 0;
printf("Amount: %d cents\n", amount);
for (int i = 0; i while (amount >= coins[i]){
amount -= coins 1;
numCoins++；
printf("Used
coin: %d cents\n", coins[i]);
}
printf("Total number of coins: %din", numCoins); return 0; }

Problem Statement 19: -#include #include int i,j,k,... Continue reading "C Programming Algorithms: Coin Change, Knapsack, MST, Shortest Path" »

LCD Interfacing with 8051

#include <reg51.h>

sbit rs = P2^0;
sbit rw = P2^1;
sbit e = P2^2;

void msdelay(unsigned int time) {
    unsigned int i, j;
    for(i = 0; i < time; i++)
        for(j = 0; j < 1275; j++);
}

void lcd_cmd(unsigned char command) {
    P1 = command;
    rs = 0;
    rw = 0;
    e = 1;
    msdelay(1);
    e = 0;
}

void lcd_init() {
    lcd_cmd(0x38); // 2 lines and 5x7 matrix
    msdelay(10);
    lcd_cmd(0x0F);
    msdelay(10);
    lcd_cmd(0x01);
    msdelay(10);
    lcd_cmd(0x80);
    msdelay(10);
}

void lcd_data(unsigned char disp_data) {
    P1 = disp_data;
    rs = 1;
    rw = 0;
    e = 1;
    msdelay(1);
    e = 0;
}

void main() {
    unsigned char a[4] = "KTU";
    int l = 0;
    lcd_init();
    while(

Introduction to Database Management Systems

A database is a structured collection of data stored on a computer system. It is managed using a Database Management System (DBMS), which provides the necessary tools for data storage, retrieval, and modification.

Core Benefits of Using a DBMS

• Reduced Data Redundancy: A DBMS helps minimize repeated data through organizational rules such as normalization.
• Enhanced Data Accuracy: The system uses specific rules, such as referential integrity, to maintain data consistency.
• Support for Multiple Users: Many people can access and use the database simultaneously without encountering operational problems.

Centralized vs. Distributed Databases

• Centralized: All data is stored in a single, primary location. This setup

Connecting via SSH

Connect to a server (default port 22):

$ ssh [email protected]

Connect on a specific port:

$ ssh [email protected] -p 6222

Connect via PEM file (requires 0400 permissions):

$ ssh -i /path/file.pem [email protected]

See: SSH Permissions

Executing Remote Commands

Execute a remote command:

$ ssh [email protected] 'ls -l'

Invoke a local script:

$ ssh [email protected] bash < script.sh

Compress and download from a server:

$ ssh [email protected] "tar cvzf - ~/source" > output.tgz

SCP File Transfers

• Copy from remote to local: scp user@server:/dir/file.ext dest/
• Copy between two servers: scp user@server:/file user@server:/dir
• Copy from local to remote: scp dest/file.ext user@server:/dir
• Copy a whole folder: scp -r user@server:/dir dest/
• Copy all files