Variables & Data Types

let declares a constant; var declares a variable you can reassign.

Example: preferring let by default

let name = "Ada"
var age = 21
print("\(name) is \(age) years old.")

Ada is 21 years old.

By now this should feel familiar: let here plays the exact same role as JavaScript's const, Kotlin's val, and Dart's final — every one of these modern languages independently converged on "prefer an unreassignable value by default" as good practice. Swift infers the type from the assigned value, or you can write it explicitly: let age: Int = 21. Note Swift's string interpolation uses backslash-parenthesis \( ), not the dollar-brace ${ } or dollar-only $name styles other languages in this tutorial use — a small but real syntax difference worth remembering.