Checkpoint: Swift the Language

Five questions on this section. Answer all of them, then see your score and why each answer is right or wrong.

What does this print?

Swift

let input = "abc"
let amount = Int(input) ?? 0
print(amount + 5)

Nothing; it doesn’t compile because Int(input) is optional.
It crashes, because “abc” isn’t a number.
abc5
5

Given func convert(_ amount: Decimal, to currency: String) -> Decimal, which call compiles?

convert(12, to: "EUR")
convert(amount: 12, to: "EUR")
convert(12, "EUR")
convert(12, currency: "EUR")

func monthlyAverage(_ amounts: [Decimal]) -> Decimal? must return nil for an empty array. Which first line is the idiomatic Swift way to handle that?

let first = amounts[0]
if amounts.isEmpty { amounts = [0] }
guard amounts.count > 0 else { print("empty") }
guard !amounts.isEmpty else { return nil }

You loop over expenses and want to count how many fall in each category, starting from an empty var counts: [String: Int] = [:]. Which line goes inside the loop?

counts[category] += 1
counts.append(category)
counts[category, default: 0] += 1
counts.insert(category)

What is result?

Swift

let values = [5, 12, 30]
let result = values.filter { $0 > 10 }.map { $0 * 2 }.reduce(0, +)

84
94
[24, 60]
42

5 questions unanswered