Swift Playground : How do I write a while function which doubles each day? - swift

Question

I need to create a loop which will show pennies each day and total for the months end. I couldn't create the loop as the playground keeps on multiplying infinitely.

Answer 1

Great question! There are definitely a lot of ways to solve this problem, but if I understand your question - this is how I would solve it.
Step 1 - Date Extension
First, I would start by making an extension to Date.
extension Date {
/// The month component of the provided date.
var month: Int {
return Calendar.current.component(.month, from: self)
}
/// Exactly one day before the provided date.
var prevDay: Date {
return Calendar.current.date(byAdding: .day, value: -1, to: self)!
}
/// Exactly one day after the provided date.
var nextDay: Date {
return Calendar.current.date(byAdding: .day, value: 1, to: self)!
}
}
These variables will make some of the later work, easier.
Step 2 - Variables
Then we can setup the variables.
First, we get the start date - I am just instantiating a new Date object which defaults to right now.
Along with that, we will define a variable where we can keep track of where we are in the iteration.
Next, we need somewhere to keep track of the values over time.
Lastly, a value to hold the starting value.
let startDate = Date() // Today, now.
var iterDate = startDate
var vals: [Date: Int] = [:]
let startingValue: Int = 1
Step 3 - The Loop
Now, the fun part - the loop. This part will be documented in the code.
// Execute the loop until the end of the start date's month.
while iterDate.month == startDate.month {
// First, check if this is the first iteration -
if vals.count == 0 {
// If so, there is nothing to double, so we just set the starting value.
vals[iterDate] = startingValue
} else {
// If there are already values - get the previous days value, double it, and save.
if let val = vals[iterDate.prevDay] {
vals[iterDate] = val * 2
}
}
// Lastly, move to the next day.
iterDate = iterDate.nextDay
}
Step 4 - Final Value
Now that we have a dictionary of all of the values, as they grow, we can get the month-end value. First, sort the dictionary - then get the value. Getting the value this way means that you don't need to know the date.
let sortedVals = vals.sorted(by: { $0.0 < $1.0 })
if let monthEnd = sortedVals.last {
let monthEndVal = monthEnd.1
// Use the value, here.
}
There it is - hope that solves the problem!
Full Code
import Foundation
extension Date {
/// The month component of the provided date.
var month: Int {
return Calendar.current.component(.month, from: self)
}
/// Exactly one day before the provided date.
var prevDay: Date {
return Calendar.current.date(byAdding: .day, value: -1, to: self)!
}
/// Exactly one day after the provided date.
var nextDay: Date {
return Calendar.current.date(byAdding: .day, value: 1, to: self)!
}
}
let startDate = Date() // Today, now.
var iterDate = startDate
var vals: [Date: Int] = [:]
let startingValue: Int = 1
// Execute the loop until the end of the start date's month.
while iterDate.month == startDate.month {
// First, check if this is the first iteration -
if vals.count == 0 {
// If so, there is nothing to double, so we just set the starting value.
vals[iterDate] = startingValue
} else {
// If there are already values - get the previous days value, double it, and save.
if let val = vals[iterDate.prevDay] {
vals[iterDate] = val * 2
}
}
// Lastly, move to the next day.
iterDate = iterDate.nextDay
}
let sortedVals = vals.sorted(by: { $0.0 < $1.0 })
if let monthEnd = sortedVals.last {
let monthEndVal = monthEnd.1
// Use the value, here.
}