Apple Swift 2.2- Collections And Control Flow

Front 1

Collection Types

Back 1

Swift provides three primary collection types, known as arrays, sets, and dictionaries, for storing collections of values. Arrays are ordered collections of values. Sets are unordered collections of unique values. Dictionaries are unordered collections of key-value associations.

Arrays, sets, and dictionaries in Swift are always clear about the types of values and keys that they can store. This means that you cannot insert a value of the wrong type into a collection by mistake. It also means you can be confident about the type of values you will retrieve from a collection.

Front 2

To get the 4th item out of an array, which index number do we use?

Back 2

3

Front 3

let a = [1,2,3]

a.insert(4, atIndex: 3)

The code raises an error. Why?

Back 3

The array is immutable and cannot be changed

Front 4

Given an array:

var a = [10, 1, 12, 22, 96, 14]

Which line of code removes the 5th element in the array?

Back 4

a.removeAtIndex(4)

Front 5

let a = [1, 2, 3]

a[3]

The code above crashes. Why?

Back 5

The index value provided is out of bounds

Front 6

Given an array:

let a = [2.0, 1.1, 2.3, 5.4]

What is the array's type?

Back 6

[Double]

Front 7

True of False:

An array preserves the order of its elements, i.e., it is an ordered collection.

Back 7

True

Front 8

DICTIONARIES

Back 8

l

Front 9

Given the following dictionary:

let dict = [1: "someValue", 2: "anotherValue"]

What is the dictionary's type?

Back 9

[Int : String]

Front 10

Given the following code:

var dict = [1: "someValue", 2: "anotherValue"]

dict.updateValue("yetAnoterValue", forKey: 3)

What is the result?

Back 10

We add a third key value pair to the dictionary

Front 11

When we try to access a value using a key that doesn't exist in a dictionary, what result do we get?

Back 11

A nil value

Front 12

For-In Loops

Back 12

l

Front 13

For this challenge, we're going to use a for in loop to compute the multiplication table for 6 and append the results to an array.

To start off, I've created an empty array of type Int and assigned it to a variable named results. Note that we have to explicitly declare the type here so that the compiler knows this array will hold Int values.

Your task for this step is to create a for in loop that iterates over a range. Multiplication tables typically range from 1 to 10 (with 10 included) so the range you are iterating over should go from 1 to 10.

For in loops also define a constant that temporarily stores the value in the iteration process. For the loop you're writing, name this constant multiplier.

Back 13

var results: [Int] = []

for multiplier in results {

print("\(1...10) time 6 is equal to \(1...10 * 6)") }

Front 14

Inside the body of the loop, we're going to use the multiplier to get the multiple of 6. For example, if the multiplier is 1, then the multiple is 1 times 6, which is equal to 6.

Once you have a value, append it to the results array. This way once the for loop has iterated over the entire range, the array will contain the first 10 multiples of 6.

Back 14

var results: [Int] = []

for multiplier in 1...10 {

results.append(multiplier * 6)

}

So here we start with the results array they give us. Now we're going to go through the range 1 to 10 as specified by the challenge. Every time through we're going to append the multiplier times 6. Our results array should end up looking like this: [6, 12, 18, 24, 30, 36, 42, 48, 54, 60]

Front 15

WHILE LOOP

Back 15

Sometimes we need to perform a set of actions while a condition is true. We don't have a predefined number of times, we just know that until the condition stops being true, we keep carrying out the action. In Swift this kind of logic is modeled with a set of while loops.

Front 16

While Loop

Back 16

/

Front 17

Which of the following comparison operators is known as the “less than or equal to” operator?

Back 17

<=

Front 18

var isAvailable = true

var isCheap = true

var status: String

if !isCheap && !isAvailable {

status = "super rare"

} else if isCheap && isAvailable {

status = "not rare"

} else if !isCheap && isAvailable {

status = "somewhat rare"

} else {

status = "common"

}

What does status evaluate to?

Back 18

"not rare"

Front 19

Both the AND and OR operators use short circuit evaluation

True or false?

Back 19

TRUE

Front 20

What does the following statement evaluate to? (!true || !false) && (true && !false)

Back 20

TRUE