Before we jump into building the app that we will be creating in later chapters, called Let's Eat, we need to understand the basics of Swift. An easy way to experiment with Swift is to use Playgrounds. It is an interactive coding environment that evaluates your code and displays the results. Using Playgrounds gives us the ability to work with Swift without needing to create a project. It is great for prototyping a particular part of your app. So, whether you are learning or experimenting, Playgrounds are an invaluable tool. To create a Playground, we need to launch Xcode and click on Get started with a playground:

The Playground template screen appears. Make sure that you select iOS, and then choose Blank and hit Next:

You will be asked to give your project a name and a location to save the file; name your new project...

Swift offers a collection of built-in data types. Its data types are a string, an integer, floating-point numbers, and Booleans. These data types are found in most programming languages. Therefore, if you are not new to programming, you can skip this section and start at the Variables and constants – where data is held section later.

Let's walk through each data type for those of you who are new to programming or would like a refresher.

The first data type we will cover is a string. A series of characters represent a string. Strings are used to display text in an app. A string wrapped in quotes is known as a string literal. In programming, we cannot just add text to...

Swift is a type-safe language, which means that you are encouraged to be clear about the value types with which your code works. Type inference means that, before your code runs, it quickly checks to ensure that you did not set anything to a different type. If you do, Xcode gives you an error. Why is this good? Let's say that you have an app in the store and that you set one of your variables as a String in one part of your code, but then accidentally set the same variable as an Int in another part of your code. This error may cause some bad behavior in your app that could cause it to crash. Finding these kinds of errors is like finding a needle in a haystack. Therefore, type checking helps you write safer code by helping you to avoid errors when working with different types.

We have now looked at data types and know that strings are for textual...

In our Playground, we know that age is an int, but with Int, we also can write arithmetic expressions using numbers, variables/constants, operators, and parentheses. Let's start with addition, subtraction, multiplication, and division. Add the following into Xcode:

So, sum added two integers (+ operator) together, totaling 43 in our preceding example. Then, we subtracted (- operator) sum from 32 to create a result (−11, in our example). After that, we took the result and multiplied (* operator) it by 5 (see -55 in the Results Panel). All of this is pretty basic math; however, you may have noticed something different with our division equation (/ operator). When you divide two integers, the result is the third integer. So, instead of -55 divided by 10 equals -5.5, our result was -5. To get the correct floating-point value of -5.5, we need...

We have hit the basics and, from this point, if you are new to programming, it is a good idea to make sure that you understand each topic we cover. As the chapters progress, we will cover more and more, so take your time and make sure that you are comfortable with all of the topics covered in this chapter.