Swift Programming

Variables Series · Lesson 5

Variables vs Constants

Learn when data should remain fixed with constants and when it should stay editable with variables.

Swift Programming Xcode iOS

What to focus on while watching

Use let for values that should not change.
Use var when updates are expected in your app flow.
Defaulting to constants can reduce accidental state changes.

Part 4: Practical Example View Variables Module

Lesson Notes and Walkthrough

By now you know how to create variables. This lesson answers the next key question: Should this value be changeable or fixed?

Core Rule

Use let when the value should stay the same.
Use var when the value needs to change over time.

Simple Comparison

let appName = "BudgetBuddy"   // fixed
var currentBalance = 120.0    // can change

currentBalance = 95.5

How to Decide as a Beginner

Ask: “Will this value ever change after setup?”
If no, start with let.
If yes, use var.

Why Prefer `let` by Default

It prevents accidental changes.
It makes your code easier to reason about.
It reduces bugs in larger projects.

Common Mistake

Beginners often declare everything with var. A better habit is to start with let, then switch to var only when the compiler tells you a reassignment is needed.

What is an Array?

Conceptual Overview

Programming

Array Programming

Coding Tutorial

Programming

Practical Example

Series| Part 4

Practice: Variables vs Constants

~5 min Beginner

Goal: Use let for fixed values and var for changing values.

Steps

Declare app name as a constant.
Declare user score as a variable and update it.
Print both to verify behavior.

Expected Output

SwiftQuest score: 15

Need a hint?

Use let appName = "SwiftQuest" and update var score.

Code

import Foundation

let appName = "SwiftQuest"
var score = 10
score = 15

print("\(appName) score: \(score)")