1️⃣Variables and Constants

Fall 2023 | Vin Bui

In almost any program that we create, we will need to store data at some point. In Swift, we can store data in two ways: variables and constants. We can think of both variables and constants as a box holding some value inside. However, there is one key difference between these two. A variable can change its value whenever we want. On the contrary, a constant can hold a value once and can never be changed again.

It may seem pointless to have both variables and constants; however, there are many advantages. If Xcode knows that a value will never change, it will optimize our program to make it run faster. Another advantage is that if we were to make a mistake and change a value of a constant when we don’t need to, Xcode will tell us and our code will not compile.


To create a variable, we use the var keyword.

var instructor = "Vin"

To change the value of the variable, we can simply do the following.

var instructor = "Vin"
instructor = "Richie"

Let’s try this in the Xcode playground.

Notice how we do not need to use the var keyword the second time. We should only use the var keyword if we are declaring a new variable. We can test this out in the Xcode playground.


Now, what if we wanted to use a constant instead of a variable? All we would need to do is to use the let keyword instead.

As we can see, changing the instructor variable to a constant caused Xcode to get angry. The error message clearly informs us that we are attempting to change the value of a constant.

It is also convention to use camelCase with Swift!

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