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Algorithms

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Algorithms (4.1)

Information Technology 9626

Pseudocode, Variables, Conditional Branching, Loops, and Procedures

Interactive Revision Notes with Self-Testing

What is an Algorithm?
Variables and Data Storage
Input and Output
Conditional Branching (IF...THEN...ELSE and CASE)
Loops
Nested Loops
Procedures and Subroutines
Common Errors
Summary and Review

1. What is an Algorithm?

Learning Objectives:

Understand what an algorithm is and why it matters
Know the structure of algorithms (input, processing, output)
Understand pseudocode and why we use it
Learn how algorithms differ from programming languages

Definition of Algorithm

Algorithm: A set of instructions sequenced to solve a problem or to represent a calculation. In computer science, an algorithm is a list of precise steps that must be carried out in a specific order. The order is crucial—it determines how the algorithm works.

Key Characteristics

Important Algorithm Properties:

Sequence: Instructions are followed one after another, from first to last
Order matters: The sequence of steps is CRUCIAL to how it works
Caters for scenarios: Must handle all possible situations and edge cases
Clear conditions: Any decisions must have clear, unambiguous conditions
Input → Processing → Output: Data enters, is processed, then results exit

Pseudocode: What and Why

Pseudocode: A structured way of writing algorithms that is independent of any programming language. It uses keywords and structure that look like a programming language but is designed for human readability.

Why use pseudocode?

Not specific to any programming language (portable)
Easy to understand and follow logic
Once written and verified, can be easily translated to any programming language
Focuses on logic rather than syntax details

Ways to Write Algorithms

Algorithm Formats:

Natural language: English instructions (can be ambiguous, not ideal for complex algorithms)
Pseudocode: Structured format (best for teaching and planning)
Flowcharts: Diagrammatic representation with symbols (Chapter 4.2)
Programming languages: Python, Java, C++, etc. (actual executable code)

Structure: Input, Processing, Output

Every algorithm typically follows this pattern:

Example: Calculator Algorithm

Process: Calculate 42 × 36

1. INPUT: Type in the two numbers (42 and 36)

2. PROCESS: Calculate 42 × 36 = 1512

3. OUTPUT: Display the result (1512) on screen

2. Variables and Data Storage

What is a Variable?

Variable: A named location in the computer's memory that stores one item of data (a number, text, etc.). Think of it as a labeled box that holds a value.

Key benefit: Using variables makes algorithms flexible. Instead of hardcoding specific numbers, you can use variable names that work with ANY values.

Assigning Values to Variables

Use the arrow symbol ← to assign values:

X ← 42

This means: store the value 42 in variable X

Variables in Calculations

You can also assign calculation results to variables:

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Also in the full note

3. Input and Output
4. Conditional Branching (Decisions)
5. Loops
6. Nested Loops
7. Procedures and Subroutines
8. Common Errors
9. Summary and Review
Algorithms: Complete Overview

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