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 changing a value that should not be changed. Another really good 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 accidentally change the value midway through your app. Apple recommends that you use let whenever possible. Typically, I will use a 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.