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

Sudoku Solver Implementation

private boolean isValid(int r, int c, int n) {
  boolean valid = true;
  int sr, sc, fr, fc;
  for (int i = 0; i < 9 && valid; i++) {
    if (i != r) if (grid[i][c] == n) valid = false;
    if (i != c) if (grid[r][i] == n) valid = false;
  }
  if (valid) {
    sr = (r / 3) * 3; fr = sr + 3; sc = (c / 3) * 3; fc = sc + 3;
    for (int i = sr; i < fr && valid; i++) {
      for (int j = sc; j < fc && valid; j++) {
        if (grid[i][j] == n) valid = false;
      }
    }
  }
  return valid;
}

private boolean solveRec(int row, int col) {
  boolean solved = false;
  if (row == 9) solved = true;
  else {
    if (grid[row][col] == 0) {
      for (int i = 1; i < 10; i++) {
        if

Understanding CSS text-overflow

The text-overflow property in CSS specifies how overflowed content that is not displayed should be signaled to the user. It works only when text exceeds the container size.

Required Conditions

To use text-overflow, the following properties must be applied:

• overflow: hidden;
• white-space: nowrap;
• Fixed width

Values of text-overflow

• clip: Default behavior; cuts off text without showing any symbol.
• ellipsis: Shows “...” at the end of truncated text.

<style>
.clipText { width: 200px; white-space: nowrap; overflow: hidden; text-overflow: clip; border: 1px solid #000; }
.ellipsisText { width: 200px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; border: 1px solid red; }
</style>
<div class=

🔎 Threat Actors & Their Attack Paths

Who is attacking?

Threat Actors are the people or groups launching attacks. Mnemonic: “NO HIS” (Nation-State, Organized Crime, Hacktivists, Insiders, Script Kiddies).

How do threats reach systems?

Threat Vectors are the attack paths used by threat actors. Mnemonic: “MFWDVN” (Messages, Files, Websites, Devices, Vendors, Networks).

Leap Year

#include <stdio.h>
int main() {
    int y;
    scanf("%d", &y);
    if ((y % 4 == 0 && y % 100 != 0) || y % 400 == 0)
        printf("Leap Year");
    else
        printf("Not Leap Year");
    return 0;
}

Simple Calculator Using Switch

#include <stdio.h>
int main() {
    char op;
    float a, b;
    scanf(" %c %f %f", &op, &a, &b);
    switch (op) {
        case '+': printf("%.2f", a + b); break;
        case '-': printf("%.2f", a - b); break;
        case '*': printf("%.2f", a * b); break;
        case '/':
            if (b != 0)
                printf("%.2f", a / b);
            else
                printf("Error");
            break;
        default: printf("Invalid Operator");
    }
    return

Postfix evaluation 

#include<stdio.H>
int stack[20];
int top = -1;

void push(int x)
{
    stack[++top] = x;
}

int pop()
{
    return stack[top--];
}

int main()
{
    char exp[20];
    char *e;
    int n1,n2,n3,num;
    printf("Enter the expression :: ");
    scanf("%s",exp);
    e = exp;
    while(*e != '\0')
    {
        if(isdigit(*e))
        {
            num = *e - 48;
            push(num);
        }
        else
        {
            n1 = pop();
            n2 = pop();
            switch(*e)
            {
            case '+':
            {
                n3 = n1 + n2;
                break;
            }
            case '-':
            {
 ... Continue reading "Ec lab" »

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 <

Addition of Two Numbers

<?php
if(isset($_POST['n1']) && isset($_POST['n2'])){
    $n1 = $_POST['n1'];
    $n2 = $_POST['n2'];
    $res = $n1 + $n2;
    echo "<h3>User Input Numbers:</h3>";
    echo "First Number = $n1 <br>";
    echo "Second Number = $n2 <br>";
    echo "Sum = $res";
}
?>

Enter Two Numbers:

PHP Conditional, Loops and Arrays Example

<?php
echo "<h3>Loop Example (1 to 5):</h3>";
for($i=1;$i<=5;$i++){
    echo "Number: $i <br>";
}
echo "<h3>Array Example:</h3>";
$fruits = array("Apple","Banana","Mango","Orange");
foreach($fruits as $f){
    echo "$f<br>";
}
?>

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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