Quiz — totals

enum Category: CaseIterable { case food, taxi }
struct Expense {
    let category: Category
    let cost: Double
}
let ride = Expense(category: .taxi, cost: 3.5)
let lunch = Expense(category: .food, cost: 2)
var totals: [Category: Double] = [:]
for e in [ride, lunch, ride] {
    totals[e.category, default: 0] += e.cost
}
print(Category.allCases.map { totals[$0, default: 0] })