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Swift 4 Programming Cookbook

For loops are great when you know how many times you intend to loop, but if you want to loop until a certain condition is met, you need a while loop.
A while loop has the following syntax:
while <#boolean expression#> { <#code to execute#> }
The code block will execute over and over until the Boolean expression returns false
. Therefore, it's a common pattern to change the current state in the code block that may cause the Boolean expression to change to false
.
If there is no chance that the Boolean expression can become true, the code will loop forever, which can lock up your app.
Let's work out how many times in a row we can flip a coin and get heads.
To flip our coin, we will need to randomly pick either heads or tails, so we will need to use a random number generator from the Foundation framework. We will discuss Foundation further in Chapter 5, Beyond the Standard Library, but for now, we just need to import the Foundation framework:
import Foundation...