Why constants versus variables?

You might be asking yourself "Why would you ever want to make something constant?". Since constants cannot change after you run your app, they keep you from accidentally breaking a value that should not change. Another excellent use for constants is for base URLs, as you would not want these to change. When you are getting data, you do not want to change the value midway through your app accidentally. Apple recommends that you use let whenever possible. Typically, I use let until Xcode warns me that a var is preferable. If I change the value from let to var, then I am verifying that this is the behavior I want.