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

Lexer Implementation (lexer.l)

%{ #include "y.tab.h" %} %%% "+" { return PLUS; } "-" { return MINUS; } "*" { return MULTIPLY; } "/" { return DIVIDE; } "%" { return MODULUS; } "(" { return LPAREN; } ")" { return RPAREN; } [0-9]+ { yylval.num = atoi(yytext); return NUMBER; } [a-zA-Z][a-zA-Z0-9]* { yylval.id = strdup(yytext); return IDENTIFIER; } [ \t\n] { /* ignore whitespace */ } . { return yytext[0]; } %%%

Parser Implementation (parser.y)

%{ #include <stdio.h> #include <stdlib.h> #include <string.h> void yyerror(const char *s); int yylex(); int temp_count = 0; int label_count = 0; void gen(char op, int arg1, int arg2, int result) { printf("%d: %c, %d, %d, %d\n", label_count++, op, arg1, arg2, result); } int new_temp() { return

Inserting the First Element into a Tree Structure

Method to add the first element (root) to a Tree Structure:

public void insertFirstNode(Object item)
{
    // If the tree is empty, the new node becomes the root of the tree
    if (theRoot == null)
    {
        Node theNewNode = new Node(item);
        theRoot = theNewNode;
    }
}

Deleting an Element from a Linked List

Method to remove an element at a specific index in a Linked List:

public void remove(int index) {
    // Special case: removing at the head of the list
    if (index == 1) {
        head = head.getNext();
    } else {
        // Find the previous and current node
        setCurrent(index);
        prev.setNext(curr.getNext());
    }
    size = size - 1;
}

Steps for Inserting an Element

Implementação da Transposição de Matriz 4x4 em C

Este programa em C demonstra como calcular e exibir a matriz transposta (B) de uma matriz quadrada de ordem 4 (A). A transposição é realizada trocando as linhas pelas colunas, ou seja, o elemento na posição A[i][j] é copiado para B[j][i].

Código Fonte em C para Transposição de Matriz

O código utiliza as bibliotecas padrão stdio.h para entrada/saída e conio.h (comum em ambientes legados) para controle de console.

#include <stdio.h>
#include <conio.h>

int main()
{
    int i, j, A[4][4], B[4][4];

    // 1. Entrada de Dados
    printf("Insira os elementos da Matriz A (4x4):\n");
    for(i = 0; i < 4; i++)
    {
        for(j = 0; j < 4; j++)
        {
            printf(

Kernel Fundamentals

Kernel = FLIH (interrupt controller) + dispatcher + communication, synchronization and mutual exclusion.

Process States

States: Ready, Running, Blocked

Transitions:

• Creation → Ready (OS creates it)
• Ready → Running (dispatcher gives it the CPU)
• Running → Ready (time slice ends)
• Running → Blocked (waits for I/O)
• Blocked → Ready (awaited event happens)
• Running → Finished

Process Control Block (PCB)

PCB: PID, state, context (PC, flags, general registers, memory access registers) + scheduling info (priority).

Interrupt Handling

FLIH: store context → find which device interrupted (poll devices by priority) → run ISR.

Chain: hardware stores PC → FLIH → ISR → dispatcher

The Dispatcher

Dispatcher: called after an interrupt changes... Continue reading "Operating Systems Kernel, Processes, Sockets, Pipes and Signals Explained" »

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"];

JDBC Driver Types

Type 1: JDBC-ODBC Bridge

• Converts JDBC calls to ODBC
• ❌ Slow, platform dependent, and obsolete

Type 2: Native API Driver

• Uses database-specific native libraries
• ⚠️ Faster than Type 1 but platform dependent

Type 3: Network Protocol Driver

• Uses middleware server to connect
• 🌐 Platform independent but slower due to network

Type 4: Thin Driver

• Directly connects to database using pure Java
• ✅ Fast, platform independent, and most used

Tags in JSP

1. Directive Tags

• Provide instructions to the JSP container
• Syntax: <%@ ... %>
• Example: page, include, taglib

2. Scripting Tags

• Scriptlet Tag: Write Java code <% ... %>
• Expression Tag: Display output <%= ... %>
• Declaration Tag: Declare variables or methods <%! ... %>

3. Action

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

FCFS and SJF CPU Scheduling C Program Example

Corrected and formatted C source code for FCFS and SJF scheduling.

FCFS Scheduling C Implementation

#include <stdio.h>

int FCFS() {
    int bt[15], n, i, wt[15];
    float twt = 0, tat = 0, att, awt;
    printf("\nTHE FCFS SCHEDULING\n");
    printf("Enter the number of processes: ");
    scanf("%d", &n);
    printf("Enter burst time of all the processes:\n");
    for (i = 0; i < n; i++) {
        printf("P%d: ", i + 1);
        scanf("%d", &bt[i]);
    }

    wt[0] = 0;
    // for calculating waiting time of each process
    for (i = 1; i < n; i++)
        wt[i] = bt[i - 1] + wt[i - 1];

    printf("ProcessID\tBurstTime\tWaitingTime\tTurn Around Time\n");
    for (i = 0; i <

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]