Unit 11.4A · Term 4

Basic Algorithmic Structures & System Programming (PHP)

Every algorithm is built from three fundamental structures: sequence, selection, and iteration. We will first review these in Pseudocode and C++, and then apply them in PHP to build a database-connected project.

Learning Objectives

11.5.3.9 Describe and apply the sequential structure
11.5.3.10 Describe and apply the branching structure
11.5.3.11 Describe and apply the loop structure
PHP.1 Write a program code using algorithmic structures in PHP
PHP.2 Connect a PHP application to a database for data storage

Lesson Presentations

11.4A-algorithmic-structures.pdf & php (1).pptx · Slides for classroom use

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Conceptual Anchor

The Recipe Analogy

Think of an algorithm as a cooking recipe. A sequence is doing steps in order (chop, mix, cook). A branch is a decision: "If the sauce is too thick, add water." A loop is repetition: "Stir every 2 minutes until golden." Every recipe — and every algorithm — uses combinations of these three structures.

Programming Constructs (Craig'n'Dave)

A clear, A-Level standard explanation of Sequence, Selection, Iteration, and Nested Structures from Craig'n'Dave.

Rules & Theory: Pseudocode & C++

1. Sequential Structure

Statements are executed one after another, in the order they appear. There are no decisions or repetitions — just straight-line execution.

Fig 1. Flowchart representation of a Sequence

Pseudocode:

INPUT radius
area ← 3.14159 * radius * radius
OUTPUT "Area = ", area

C++:

#include <iostream>
using namespace std;

int main() {
    double radius;
    cout << "Enter radius: ";
    cin >> radius;
    double area = 3.14159 * radius * radius;
    cout << "Area = " << area << endl;
    return 0;
}

2. Branching Structure (Selection)

The program makes a decision based on a condition. If the condition is TRUE, one path is taken; otherwise, an alternative path is followed.

Fig 2. Flowchart representation of Branching (Selection)

Pseudocode (IF/ELSE):

INPUT mark
IF mark >= 50 THEN
    OUTPUT "Pass"
ELSE
    OUTPUT "Fail"
ENDIF

C++ (switch):

char grade;
cin >> grade;
switch (grade) {
    case 'A': cout << "Excellent"; break;
    case 'B': cout << "Good";      break;
    case 'C': cout << "Satisfactory"; break;
    default:  cout << "Below standard";
}

3. Loop Structure (Iteration)

A group of statements is repeated while a condition is met (or a fixed number of times).

Pre-condition (WHILE)

Post-condition (REPEAT/UNTIL)

Fig 3. Control flow in Pre-condition vs Post-condition loops

FOR loop — Pseudocode:

FOR i ← 1 TO 5
    OUTPUT i
NEXT i

WHILE loop — Pseudocode:

total ← 0
INPUT num
WHILE num <> -1
    total ← total + num
    INPUT num
ENDWHILE
OUTPUT "Total = ", total

Algorithmic Structures Overview: Sequence, Selection, Iteration

Worked Examples (Trace Tables)

1 Tracing a Loop

a ← 10
b ← 3
WHILE a > 0
    a ← a - b
    OUTPUT a
ENDWHILE

a	b	a > 0	OUTPUT
10	3	TRUE
7		TRUE	7
4		TRUE	4
1		TRUE	1
-2		FALSE	-2

Code Execution & Trace Tables Visualization

Term Project: School Student Registration System

Criteria	Detailed Description	Marks
Core Functionality (PHP-Based)	Fully working PHP system: form handling, data storage (file/MySQL), navigation, and validation.	1
Sequential Structure (PHP Logic)	Clear multi-step processing in PHP (input → sanitization → validation → storage → output). Well-commented.	1
Conditional Statements	Effective use of if/else, elseif, or switch. Includes input validation, error handling, and branching logic.	2
Nested Conditional Statements	Use of nested if/else for complex validation (e.g., checking multiple conditions, duplicate IDs, etc.).	1
Loops (Iteration)	Use of loops (while, for, foreach) to process or display multiple records dynamically.	1
Nested Loops	Advanced use of nested loops (e.g., table generation, multi-dimensional data handling).	2
Code Quality & PHP Practices	Readable PHP code, proper structure, meaningful variables, comments explaining algorithmic logic.	1
User Interface & Experience	Clean layout, easy navigation, clear feedback messages.	1
Documentation (Algorithm Focused)	Clear explanation of where each structure is used (sequential, loops, conditionals, nested). Screenshots included.	1
Creativity & Advanced Features (Bonus)	Search/filter, edit/delete, login system, or database integration.	1
Total Marks:		12

Project Prep: Algorithmic Structures in PHP & Database

1. PHP Variables & Syntax

<?php
$name = "John"; // String
$age = 20;      // Integer
echo "Student: " . $name;
?>

2. Branching & Nested Conditionals (For Validation)

This helps you score marks in Conditional Statements and Nested Conditional Statements.

<?php
$score = 85;
$hasID = true;

// Nested Conditional Statement
if ($hasID == true) {
    if ($score >= 90) {
        echo "A";
    } elseif ($score >= 70) {
        echo "B";
    } else {
        echo "C";
    }
} else {
    echo "Error: No ID found.";
}
?>

3. Loops & Nested Loops (For HTML Tables)

This helps you score marks in Loops and Nested Loops.

<?php
// Nested loops to generate a grid/table
echo "<table border='1'>";
for ($row = 1; $row <= 3; $row++) {
    echo "<tr>";
    for ($col = 1; $col <= 2; $col++) {
        echo "<td>Row $row, Col $col</td>";
    }
    echo "</tr>";
}
echo "</table>";
?>

4. Core Functionality: HTML Forms & Database Connection (MySQL)

Form Handling: Data sent from an HTML form using method="POST" is retrieved using the $_POST array.

Database Connection: Use mysqli_connect() to store your form data permanently into a MySQL database.

<!-- 1. HTML Form -->
<form method="POST" action="">
    Name: <input type="text" name="studentName" required>
    <input type="submit" value="Register">
</form>

<?php
// 2. PHP Sequential Processing & Database Connection
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    
    // Step A: Sanitization
    $name = $_POST['studentName'];
    
    // Step B: Database Connection Details
    $host = "localhost";
    $user = "root";
    $pass = "";
    $dbname = "school_db";
    
    // Step C: Connect
    $conn = mysqli_connect($host, $user, $pass, $dbname);
    
    // Step D: Nested Conditional Validation
    if (!$conn) {
        die("Connection failed: " . mysqli_connect_error());
    } else {
        if (!empty($name)) {
            // Step E: Insert Query
            $sql = "INSERT INTO students (name) VALUES ('$name')";
            if (mysqli_query($conn, $sql)) {
                echo "New record created successfully";
            }
        } else {
            echo "Name cannot be empty";
        }
    }
    // Step F: Close Connection
    mysqli_close($conn);
}
?>

Project Tip

To get maximum marks, ensure you clearly comment your code. Label where you are using Sequential, Selection, and Iteration so the examiner can see you hit the rubric criteria.

Tasks

Remember

Name the three basic algorithmic structures and describe how the $_POST method retrieves data.

Apply

Write a PHP script to connect to a database named "library_db" and display an error message if the connection fails using an IF statement.

Analyze

A student wrote: FOR i ← 1 TO 10 ... NEXT i but inside the loop also has i ← i + 1. Trace the execution and explain what goes wrong.

Create (Project Start)

Set up your local server (XAMPP/MAMP). Create your HTML Registration Form and establish a blank PHP file that successfully connects to your local database.

Self-Check Quiz

Q1: Which flowchart shape represents a decision?

Diamond (rhombus)

Q2: Which PHP function is used to establish a connection to a MySQL database?

mysqli_connect()

Q3: Fix the error in the following PHP code: echo "Hello"

Missing semicolon at the end: echo "Hello";

Reflection & Homework

Reflection: What did you learn today? What aspect of the project rubric seems the most challenging?