let and var are some of the most common keywords used in Swift
let keyword in Swift defines a constant.
let favoriteFood = "eggs"
Constants cannot be changed. You cannot change the value of
favoriteFood above once you have set it.
If you try to change a constant you will get an error. Try this:
let favoriteFood = "eggs" favoriteFood = "fries"
You will get an error that says
Cannot assign to value: 'favoriteFood' is a 'let' constant.
var keyword in Swift defines variables.
var dinner = "pizza"
Variables can be changed.
var dinner = "pizza" dinner = "rice"
If you know the value of something won’t change, I recommend you set it as a constant. This prevents you or your teammate from changing the value by accident. Constants also allow the compiler to perform some optimizations to your code as well.