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

Operating Systems: System Calls and File Descriptors

int main(int argc, char *argv[]) {
  int fd = open(argv[1], O_WRONLY | O_CREAT | O_EXCL, 0644);
  if (fd == -1) {
    printf("There was a problem creating \"%s\"!\n", argv[1]);
    return 1;
  }
  close(fd);
  return 0;
}

void copyContents(int sourceFD, int destinationFD) {
  char buffer[kCopyIncrement];
  while (true) {
    ssize_t bytesRead = read(sourceFD,

Assembly Language Code Analysis and Solutions

Section 1: Instruction Correctness Check

.data

calculate WORD 100
wVal DWORD 2

Instructions:

1. mov bl, calculate
2. mov ax, wVal

Question 1: Are the above two instructions correct? If not, justify your claim. [2 marks]

Answer:

Both instructions are incorrect.

• For the mov operation, the operands must generally be of the same size.
• In instruction 1, bl is 8 bits (1 byte), but calculate is defined as a WORD (16 bits or 2 bytes). The operand sizes do not match.
• In instruction 2, ax is 16 bits (2 bytes), but wVal is defined as a DWORD (32 bits or 4 bytes). The operand sizes do not match.

Section 2: Loop Pseudo-code

Question 2: Write the pseudo-code for the loop that calculates the sum of the integers 3 + 2 + 1. [2 marks]

P1: Python String Manipulation Techniques

Demonstrating String Operations

s = "hello"
print(s.capitalize())
print(s.upper())
print(s.rjust(100))
print(s.center(100))
print(s.replace('l','(M)'))
print(s)
print("don't")

Indexing

a = 'symbiosis2024'
print(a[2])

Negative Indexing

print(a[-1])
print(a[-6])

Slicing

print(a[9:12])
print(a[9:])
print(a[9:-1])
print(a[:8])
print(a[-12:-1])

Stride [start index:end index:step size]

print(a[0:13:2])
print(a[0::2])

Concatenation

b = 'hello'
c = 'world'
d = b + c
print(d)
e = b + " " + c
print(e)

Repetition

f = a * 3
print(f)
g = "2024"
print(g * 2)
print(a + '2')

Reversing a String

print(a[::-1])

Split

h = "sspu"
print(h.split()) # Returns a list
i = "05/08/2024"
print(i.split("/"))
j = "14:20:25"
print(j.split("

Nmap Options

-PE: Quickly check if host is up.

-sn: Disable port scanning (host discovery).

-n: Disables DNS resolution (checks IP online without looking up hostnames).

-O: OS detection.

-A: OS detection, Version detection, Script scanning, traceroute.

-sV: Service detection (banner info, version).

-vV: Provides verbose output.

-sC: Scan with default scripts for additional info gathering.

--min-rate=5000: Ensures scan sends at least 5k packets per second.

nmap --script smb-enum-shares.nse -p 445 (ip): List shares and their properties.

To see scripts starting with X: ls /path/X

To execute script with script tracing: sudo nmap -script=smb-os-discovery -script-trace target_ip

To enumerate the SMB share files: sudo nmap -script=smb-enum-shares target_ip

Vulnerability... Continue reading "Nmap, Netcat, and Metasploit Commands Cheat Sheet" »

🧾 Data Transfer Instructions

These instructions are used to move data between registers, memory, and I/O ports.

➕ Arithmetic Instructions

These instructions perform basic mathematical operations.

Steps for Training a Machine Learning Project in the Cloud

Definition: Cloud ML Project Training

Training an ML Project in the Cloud means utilizing cloud-based resources and services to build, train, and optimize a Machine Learning model.

The Seven Key Steps in Cloud ML Training

1. Data Collection: Gather and upload the dataset to cloud storage.
2. Data Preprocessing: Clean and prepare data using cloud notebooks or specialized processing services.
3. Model Selection: Choose the appropriate algorithm or utilize a pre-built model architecture.
4. Training: Use scalable cloud compute resources (GPUs/TPUs) for intensive model training.
5. Evaluation: Test model accuracy and performance using validation data.
6. Hyperparameter Tuning: Optimize model parameters for better

PHP Form Validation

To create a PHP form and perform server-side validation for user input such as name, email, and password:

<?php
$name = $email = $password = "";
$nameErr = $emailErr = $passwordErr = "";

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Name Validation
    if (empty($_POST["name"])) { $nameErr = "Name is required"; } else { $name = $_POST["name"]; }
    // Email Validation
    if (empty($_POST["email"])) { $emailErr = "Email is required"; } else { $email = $_POST["email"];
        if (!filter_var($email, FILTER_VALIDATE_EMAIL)) { $emailErr = "Invalid email format"; } 
    }
    // Password Validation
    if (empty($_POST["password"])) { $passwordErr = "Password is required"; } else { $password = $_POST["password"];

RecyclerView Features and GridView Implementation

1. List and explain any three features of RecyclerView. Develop an Android application to display any five programming languages in GridView.

• View Recycling: Reuses views to improve performance and reduce memory usage.
• ViewHolder Pattern: Stores item views to avoid repeated findViewById() calls.
• Flexible Layout: Supports LinearLayoutManager, GridLayoutManager, and StaggeredGridLayoutManager.

Example: XML and Java

Java Code:

GridView gridView = findViewById(R.id.gridView);
String[] languages = {"C", "C++", "Java", "Python", "Kotlin"};
ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, languages);
gridView.setAdapter(adapter);

API Types and Data Passing