Variables vs. Constants

The Metaphor: Imagine computer memory as a giant wall of labeled post-office boxes. Each box can hold one piece of information at a time, and you can find your data later by looking at the label!

Identifiers: The Labels

Variables and Constants are simply names we give to storage locations in memory. These names (called identifiers) help us find and use our data without remembering complex memory addresses.

• Memory Address: The actual physical location in computer RAM (like "Box #4521")
• Identifier: A meaningful name we use instead (like "Student_Age")
• Value: The actual data stored in that location

Definition: A variable is a named storage location in memory whose value can change (vary) during the execution of a program. Think of it like a container where you can put different things over time.

Real-World Examples

• Current_Score in a video game — increases or decreases as you play
• Temperature on a weather app — changes as weather conditions update
• User_Password during a login attempt — typed differently each time
• Shopping_Cart_Total — changes as you add or remove items

Why Variables Matter

Programs need to remember things that change: user input, calculated results, game states, and more. Variables give us a way to store and update this dynamic information.

Definition: A constant is a named storage location whose value remains the same throughout the entire program. Once set, it cannot be changed.

Why Use Constants?

• Prevents accidental changes: Protects critical values like tax rates
• Makes code readable: Using "PI" is clearer than "3.14159"
• Easier to update: Change one constant instead of many formulas
• Self-documenting: Shows that certain values should never change

Common Examples

• PI = 3.14159 — The ratio of a circle's circumference to its diameter
• GRAVITY = 9.8 — Earth's gravitational acceleration
• SALES_TAX = 0.15 — Jamaica's 15% GCT rate
• DAYS_IN_WEEK = 7 — Always 7, never changes

Before using a variable or constant, you must tell the computer about it. This happens in two steps:

Declaration

Declaration tells the computer the name and type of the storage location. You're creating the "box" and putting a label on it.

DECLARE Total_Score AS Integer
DECLARE PI AS Real

Initialization

Initialization gives the variable or constant its very first value. For constants, this happens at declaration. For variables, it can happen later.

SET PI = 3.14159
SET Total_Score = 0

Naming Rules (Identifiers)

• Must start with a letter (A-Z or a-z)
• Can include numbers but not at the start (e.g., score1 is OK, 1score is not)
• Cannot contain spaces (use Student_Name or studentName)
• Cannot use reserved words like IF, THEN, FOR as names
• Should be descriptive (use Player_Score instead of x or y)
• Special characters allowed: Only underscore (_) is typically allowed

Variable vs Constant Declaration

Variable: DECLARE Score AS Integer

Constant: CONSTANT TAX_RATE = 0.15

Ask yourself this simple question: "Will this value ever need to be updated while the program is running?"

Decision Logic

Examples in Context

• User's Age — Variable (might update on birthday)
• Number of Hours in a Day — Constant (always 24)
• Price of Bread — Variable (changes over time)
• Speed of Light — Constant (never changes)
• Game Level — Variable (increases as player progresses)
• Days in a Week — Constant (always 7)

When to Use Constants in Your SBA

Great job completing this module! You now understand the fundamental difference between variables and constants.

Key Differences

Remember These Rules

• Declaration: Tell the computer the name and type
• Initialization: Give the first value
• Naming: Must start with a letter, no spaces, be descriptive
• Choice: Ask "Will this change?" — Yes = Variable, No = Constant

🧠 Memory Tip:
"VARIABLE = Varies, CONSTANT = Consistent"