Last time, we learned about variables. A variable is like a labeled box where we can change what’s inside anytime we want. Now, let’s learn something a little different — a “label that never changes its value”, called a constant in Swift!
🔁 What’s the Difference Between Variables and Constants?
In Swift, there are two main ways to store information:
|
Name |
Can You Change the Value? |
Keyword Used |
|---|---|---|
|
Variable |
✅ Yes, you can change it |
var |
|
Constant |
❌ No, it can’t be changed |
let |
So, if you want a value that can change, use var.
But if the value should never change, use let.
🎂 Practice: My Birthday Never Changes!
Does your birthday change? Of course not!
It happens once a year, but the date always stays the same.
That’s why we should save it using a constant, not a variable.
let myBirthday = "2014-05-10"
print("My birthday is \(myBirthday).")Output:
My birthday is 2014-05-10.Now try to change your birthday like this:
myBirthday = "2020-01-01"Uh-oh! ❗️ Swift knows that you’re trying to change the value of a constant,
so it will show you an error message — usually in red!
Because constants should never change, Swift will stop you from changing it.
🔐 When Should You Use Constants?
Use constants when:
• You want to store information that never changes
e.g. your birthday, a fixed file name, a set value
• You want to protect a value from being changed by mistake
e.g. app settings, personal information
Think of constants as a safety shield that keeps your values safe from being changed accidentally.
✨ Wrapping Up
Today, we learned about constants (let) —
they are just like variables, but the value never changes!
Let’s remember:
• If the value can change, use var → variable
• If the value should never change, use let → constant
That’s how we decide which one to use when writing Swift code!
댓글 쓰기