Chapter 3: Types

Swift Programming from Scratch

The Swift Sandbox is integrated, making the exercises interactive. Read more about the book here.

1. First Steps
2. Conditionals
3. Types
4. Loops
5. Strings
6. Arrays
7. Functions
8. Recursion
9. Closures
10. Tuples & Enums
11. Dictionaries

Chapter 3: Types

Introduction

All the values we’ve worked with so far have been integer numbers.
All variables and constants in Swift have a type. Think of the type as describing what kind of values a variable can have. The type for integer numbers is Int.

You can see the type of a variable in Xcode by option clicking on it’s name (hold down option(⌥) and click on its name). A popup will appear were you can see the type of the variable.

Here you can see that our lucky number 7 is of type Int.

We often need variables of types that aren’t Int. You already encountered a different type. The expresssions inside an if statement. These values have type Bool also known as Boolean named after mathematician George Boole who layed out the mathematical foundations of Logic.

Comparision operators (<,<=,>,>=,==,!=) produce values of type Bool. Boolean expressions can have only one of 2 types true or false

For example

var luckyNumber = 7

var condition = 777 > luckyNumber

condition will be of type Bool and have a value of true as seen below:

The Double type

What if we want to use numbers of the form (1.5, 1.7, 1.6,...)? We can of course do that in Swift! If you declare a variable lets say heightInMeters with a value of 1.85 and check its type you’ll see that its type is Double

var heightInMeters = 1.85

Variables of type Double hold fractional numbers and can be used for calculating fractional quantities. Any number of the form X.Y is a Double Examples: (35.67, 2.0, 0.5154, …)

Doubles can be added, subtracted, multiplied and divided using the familiar operators (+, -, *, /).

There is no equivalent to the remainder(%) operator for doubles.

var a = 3.5
var b = 1.25

print(a + b) // 4.75
print(a - b) // 2.25
print(a * b) // 4.375
print(a / b) // 2.8

print(1.0 / 3.0) // 0.333333333333333

Declaring variables of a certain type

To explicitly declare a variable of a certain type you use the syntax:

var variable : Type = ...

For example:

var integer:Int = 64
var boolean:Bool = false
var double:Double = 7.2

If you don’t provide a type for a variable a type is automatically inferred for you using the value you provide

Examples:

// We don't declare a type for a it is implicitly Int 
// because the value 7 is an Int
var a = 7 

print(a / 2) // 3

// We don't declare a type for a it is implicitly Double 
// because the value 7.0 is a Double
var a = 7.0 
print(a / 2) // 3.5

If you explicilty declare a variable as having type Double then you can initialize it with an integer but the variable will hold a Double

var a:Double = 7 // We explicitly declare a type for a

print(a / 2) // 3.5

Type Casting

Initializing a variable of type Double with an integer only works if you use a constant value. If you try initializing a variable of type Double with a variable of type Int then you’ll get an error.

var a = 64
var b:Double = a // Error

To solve this problem we need to convert the value from Int to Double. Converting a value of some type to a different type is known as type casting or just casting.

To cast a variable to a certain type we use TypeName(variableName) or the as operator, variableName as TypeName. For example:

var a = 64
var b:Double = Double(a) // b = 64.0
var c:Double = a as Double // c = 64.0

Casting a Double to an Int discards all the digits after the decimal point. Note that this digits can’t be recovered by casting the variable back to Double.

Example:

var number = 5.25
var integerNumber = Int(number) // 5
var doubleNumber = Double(integerNumber) // 5.0

3.1 Average

You are given 2 Doubles a and b. Print their average.

var a = 2.0
var b = 5.0

3.5

var a = 20.0
var b = 40.0

30.0

var a = 2.0
var b = 5.0

print((a + b) / 2)

3.2 Weighted Average

You are given 3 grades stored in 3 variables of type Double finalsGrade, midtermGrade, projectGrade. These grades are used to compute the grade for a class. finalsGrade represents 50% of the grade. midtermGraderepresents 20% of the grade. projectGrade represents 30% of the final grade.
Print the grade for the class.

var finalsGrade = 2.0
var midtermGrade = 5.0
var projectGrade = 3.0

2.7

var finalsGrade = 5.0
var midtermGrade = 5.0
var projectGrade = 5.0

5.0

var finalsGrade = 2.0
var midtermGrade = 4.0
var projectGrade = 3.0

print(0.5 * finalsGrade + 0.2 * midtermGrade  + 0.3 * projectGrade)

3.3 Tipping

You have the cost of a meal at a restaurant stored in a variable mealCost of type Double.
You would like to leave a tip of a certain percentage. The percentage is stored in a variable tip of type Int.
Print the total cost of the meal.

var mealCost:Double = 3.5
var tip:Int = 20

4.2

var mealCost:Double = 10.0
var tip:Int = 10

11.0

var mealCost:Double = 3.5
var tip:Int = 20

var tipCost = mealCost * Double(tip) / 100.0
var totalCost = mealCost + tipCost

print(totalCost)

3.4 Rounding

You are given a variable number of type Double. Create a new variable called roundedNumber that has at most 1digit after the decimal dot.

var number = 5.1517

roundedNumber = 5.1

var number = 32.5

roundedNumber = 32.5

var number = 2.0

roundedNumber = 2.0

var number = 5.1517

var intNumber = Int(number * 10.0)

var roundedNumber = Double(intNumber) / 10.0

3.5 Above average

You are given three grades obtained by 3 students in a class stored in variables grade1, grade2, grade3 of typeDouble.
You are also given your grade in the class stored in a variable yourGrade of type Double.
Print above average if your grade is greater than the class average or below average” otherwise.
Note: the average of the class includes your grade.

var grade1 = 7.0
var grade2 = 9.0
var grade3 = 5.0
var yourGrade = 8.0

"above average"

var grade1 = 10.0
var grade2 = 9.0
var grade3 = 10.0
var yourGrade = 9.0

"below average"

var grade1 = 7.0
var grade2 = 9.0
var grade3 = 5.0
var yourGrade = 8.0

var averageGrade = (grade1 + grade2 + grade3 + yourGrade) / 4.0

if yourGrade > averageGrade {
    print("above average")
} else {
    print("below average")
}

3.6 Fields

A farmer is harvesting wheat from a number of wheat fields, given in a variable numberOfFields of type Int.
Each field produces the same quantity of wheat given in a variable wheatYield of type Double.
Sometimes the harvest is increased by 50% due to favorable weather conditions. You are given this information in a variable weatherWasGood of type Bool.
Print the total amount of wheat that the farmer will harvest.

var numberOfFields:Int = 5
var wheatYield:Double = 7.5
var weatherWasGood:Bool = true

56.25

var numberOfFields:Int = 5
var wheatYield:Double = 7.5
var weatherWasGood:Bool = false

37.5

var numberOfFields:Int = 5
var wheatYield:Double = 7.5
var weatherWasGood:Bool = true

var totalYield = Double(numberOfFields) * wheatYield
if (weatherWasGood == true) {
    totalYield = totalYield * 1.5
}

print(totalYield)

Swift Programming from Scratch

Read more about the book here.

1. First Steps
2. Conditionals
3. Types
4. Loops
5. Strings
6. Arrays
7. Functions
8. Recursion
9. Closures
10. Tuples & Enums
11. Dictionaries

Feel free to ask any questions in the comments bellow.