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Mastering Swift
Mastering Swift

Mastering Swift:

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Mastering Swift

Chapter 2. Learning about Variables, Constants, Strings, and Operators

The first program I ever wrote was written in the basic programming language, and was the typical Hello World application. This application was pretty exciting at first, but the excitement of printing static text wore off pretty quickly. For my second application, I used basic's input command to prompt the user for a name and then printed out a custom hello message to the user with their name in it. At the age of 12, it was pretty cool to display Hello Han Solo. This application led me to create numerous Mad Lib style applications that prompted the user for various words and then put those words into a story that was displayed after the user entered all the required words. These applications introduced me to, and taught me, the importance of variables. Every useful application I created since then has used variables.

In this chapter, we will cover the following topics:

  • What are variables and constants?
  • Difference...

Constants and variables

Constants and variables associate an identifier (such as myName or currentTemperature) with a value of a particular type (such as a String or Int) where the identifier can be used to retrieve the value. The difference between a constant and a variable is that a variable can be updated/changed while a constant cannot be.

Constants are good for defining values that you know will never change, such as the freezing temperature of water or the speed of light. Constants are also good for defining a value that we use many times throughout our application, such as a standard font size or maximum characters in a buffer. There will be numerous examples of constants throughout this book.

Variables are more common in software development than constants. You can make useful applications without using constants (although it is a good practice to use constants); however, it is almost impossible to create a useful application without variables.

You can use almost any character in...

Defining constants and variables

Constants and variables must be defined prior to using them. To define a constant, you use the keyword let, and to define a variable, you use the keyword var. The following are some examples of constants and variables:

// Constants
let freezingTemperatureOfWaterCelsius = 0
let speedOfLightKmSec = 300000

// Variables
var currentTemperature = 22
var currentSpeed = 55

We can declare multiple constants or variables in a single line by separating them with a comma. For example, we could shrink the preceding four lines of code down to two lines like this:

// Constants
let freezingTempertureOfWaterCelsius = 0, speedOfLightKmSec = 300000

// Variables
var currentTemperture = 22, currentSpeed = 55

We can change the value of a variable to another value of a compatible type; however, as we noted earlier, we cannot change the value of a constant. Let's look at the following Playground. Can you tell what is wrong with the code from the error message that is shown in...

Numeric types

Swift contains many of the standard numeric types that are suitable for storing various integer and floating-point values.

Integers

An integer is a whole number. Integers can be either signed (positive, negative, or zero) or unsigned (positive or zero). Swift provides several integer types of different sizes. The following chart shows the value ranges for the different Integer types:

Type

Minimum

Maximum

Int8

-128

127

Int16

-32,768

32,767

Int32

-2,147,483,648

2,147,483,647

Int64

- 9,223,372,036,854,775,808

9,223,372,036,854,775,807

Int

- 9,223,372,036,854,775,808

9,223,372,036,854,775,807

   

UInt8

0

255

UInt16

0

65,535

UInt32

0

4,294,967,295

UInt64

0

18,446,744,073,709,551,615

UInt

0

18,446,744,073,709,551,615

Tip

Unless there is a specific reason to define the size of an integer, I would recommend using the standard Int or UInt type. This will save you from needing to convert between different types of integers.

In Swift, Int (as...

The Boolean type

Boolean values are often referred to as logical values because they can be either true or false. Swift has a built-in Boolean type called Bool that accepts one of two built-in Boolean constants. These constants are true and false.

Boolean constants and variables can be defined like this:

let swiftIsCool = true
let swiftIsHard = false

var itIsWarm = false
var itIsRaining = true

Boolean values are especially useful when working with conditional statements, such as if and while. For example, what do you think this code would do:

let isSwiftCool = true
let isItRaining = false
if (isSwiftCool) {
    println("YEA, I cannot wait to learn it")
}

if (isItRaining) {
    println("Get a rain coat")
}

If you answered that this code would print out YEA, I cannot wait to learn it, then you would be correct. Since isSwiftCool is set to true, the YEA, I cannot wait to learn it message is printed out, but isItRaining is false; therefore, the Get a rain coat is not.

You can...

The string type

A string is an ordered collection of characters, such as Hello or Swift. In Swift, the string type represents a string. We have seen several examples of strings already in this book, so the following code should look familiar. This code shows how to define two strings:

var stringOne = "Hello"
var stringTwo = " World"

Since a string is an ordered collection of characters, we can iterate through each character of a string. The following code shows how to do this:

var stringOne = "Hello"
for char in stringOne {
  println(char)
}

The preceding code will display the results shown in the following screenshot:

The string type

There are two ways to add one string to another string. We can concatenate them or we can include them inline. To concatenate two strings, we use the + or the += operator. The following code shows how to concatenate two strings. The first example appends stringB to the end of stringA and the results are put into a new stringC variable. The second...

Optional variables

All of the variables that we have looked at so far are considered to be nonoptional variables. This means that the variables are required to have a non-nil value; however, there are times when we want or need our variables to contain nil values. This can occur if we return a nil from a function whose operation failed or if a value is not found.

In Swift, an optional variable is a variable that we are able to assign nil (no value) to. Optional variables and constants are defined using ? (question mark). Let's look at the following Playground; it shows us how to define Optional and shows what happens if we assign a nil value to a Non-Optional variable:

Optional variables

Notice the error we receive when we try to assign a nil value to the nonoptional variable. This error message tells us that the stringTwo variable does not conform to the NilLiteralConvertible protocol. What this tells us is that we are assigning a nil value to a variable or constant that is not defined as an optional...

Constants and variables


Constants and variables associate an identifier (such as myName or currentTemperature) with a value of a particular type (such as a String or Int) where the identifier can be used to retrieve the value. The difference between a constant and a variable is that a variable can be updated/changed while a constant cannot be.

Constants are good for defining values that you know will never change, such as the freezing temperature of water or the speed of light. Constants are also good for defining a value that we use many times throughout our application, such as a standard font size or maximum characters in a buffer. There will be numerous examples of constants throughout this book.

Variables are more common in software development than constants. You can make useful applications without using constants (although it is a good practice to use constants); however, it is almost impossible to create a useful application without variables.

You can use almost any character in the...

Defining constants and variables


Constants and variables must be defined prior to using them. To define a constant, you use the keyword let, and to define a variable, you use the keyword var. The following are some examples of constants and variables:

// Constants
let freezingTemperatureOfWaterCelsius = 0
let speedOfLightKmSec = 300000

// Variables
var currentTemperature = 22
var currentSpeed = 55

We can declare multiple constants or variables in a single line by separating them with a comma. For example, we could shrink the preceding four lines of code down to two lines like this:

// Constants
let freezingTempertureOfWaterCelsius = 0, speedOfLightKmSec = 300000

// Variables
var currentTemperture = 22, currentSpeed = 55

We can change the value of a variable to another value of a compatible type; however, as we noted earlier, we cannot change the value of a constant. Let's look at the following Playground. Can you tell what is wrong with the code from the error message that is shown in the...

Numeric types


Swift contains many of the standard numeric types that are suitable for storing various integer and floating-point values.

Integers

An integer is a whole number. Integers can be either signed (positive, negative, or zero) or unsigned (positive or zero). Swift provides several integer types of different sizes. The following chart shows the value ranges for the different Integer types:

Type

Minimum

Maximum

Int8

-128

127

Int16

-32,768

32,767

Int32

-2,147,483,648

2,147,483,647

Int64

- 9,223,372,036,854,775,808

9,223,372,036,854,775,807

Int

- 9,223,372,036,854,775,808

9,223,372,036,854,775,807

   

UInt8

0

255

UInt16

0

65,535

UInt32

0

4,294,967,295

UInt64

0

18,446,744,073,709,551,615

UInt

0

18,446,744,073,709,551,615

Tip

Unless there is a specific reason to define the size of an integer, I would recommend using the standard Int or UInt type. This will save you from needing to convert between different types of integers.

In Swift, Int (as well as other numerical...

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Description

If you are a developer that learns best by looking at, and working with, code, then this book is for you. A basic understanding of Apple's tools is beneficial but not mandatory.

What you will learn

  • Prototype and test code in a Playground
  • Understand the basics of Swift, including operators, collections, control flows, and functions
  • Create and use Classes, Structures, and Enums, including objectoriented topics such as inheritance, protocols, and Extensions
  • Dwell into Subscripts, Optionals, and closures with realworld scenarios
  • Employ Grand Central Dispatch to add concurrency to your applications
  • Study the ObjectiveC interoperability with mix and match
  • Access network resources using Swift
  • Implement various standard design patterns in the Swift language

Product Details

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Publication date, Length, Edition, Language, ISBN-13
Publication date : Jun 29, 2015
Length: 358 pages
Edition : 1st
Language : English
ISBN-13 : 9781784392154
Vendor :
Apple
Category :
Languages :
Tools :

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Product Details

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Length: 358 pages
Edition : 1st
Language : English
ISBN-13 : 9781784392154
Vendor :
Apple
Category :
Languages :
Tools :

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Table of Contents

16 Chapters
1. Taking the First Steps with Swift Chevron down icon Chevron up icon
2. Learning about Variables, Constants, Strings, and Operators Chevron down icon Chevron up icon
3. Using Collections and Cocoa Data Types Chevron down icon Chevron up icon
4. Control Flow and Functions Chevron down icon Chevron up icon
5. Classes and Structures Chevron down icon Chevron up icon
6. Working with XML and JSON Data Chevron down icon Chevron up icon
7. Custom Subscripting Chevron down icon Chevron up icon
8. Using Optional Type and Optional Chaining Chevron down icon Chevron up icon
9. Working with Generics Chevron down icon Chevron up icon
10. Working with Closures Chevron down icon Chevron up icon
11. Using Mix and Match Chevron down icon Chevron up icon
12. Concurrency and Parallelism in Swift Chevron down icon Chevron up icon
13. Swift Formatting and Style Guide Chevron down icon Chevron up icon
14. Network Development with Swift Chevron down icon Chevron up icon
15. Adopting Design Patterns in Swift Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Full star icon Full star icon 5
(2 Ratings)
5 star 100%
4 star 0%
3 star 0%
2 star 0%
1 star 0%
Just Me Dec 20, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Great book for learning Swift 1.x but if your are looking for a book on Swift 2 get the Mastering Swift 2 book
Amazon Verified review Amazon
Amazon Customer Dec 04, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Mastering Swift is a very clear and concise. Really nice to anyone who wants to jump from Objective C to Swift or start from the scratch.All the explanations are followed with clear example.You won't regret it.
Amazon Verified review Amazon
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