Swift - using my variables in an "if" statement

Question

I’m trying to use the if statement below (I commented it out). The code works perfectly except that when I “uncomment” it, I get an error. Please help me with this issue and if you have any advice on things you’d change, please let me know as I’d rather not make a bad habit of things that should be done differently.

On that note, if you were born in the 1900’s and would like to try this code, please feel free! It’ll tell you the day of the week you were born on. Unless you were born in January or February (that’s why I need the if statement fixed). Also, if you know where and when to add enums for the arguments called in the function (the day, month and year), that would be awesome as well.

class Birthday {
    func findDayOfWeek(_ month:Int, _ day:Int, _ year:Int) -> String{
        var runningNumber = 0

        //print( "start with " , runningNumber)

        let shortenedYear = (year - 1900)
        let remainder = shortenedYear % 12

        runningNumber += remainder

        //print("add the remainder" , runningNumber)    

        var testNumber = runningNumber

        while testNumber > 3 {
            runningNumber += 1
            testNumber -= 4
        }

        //print("because we added one for every four" ,runningNumber)

        let dividedByTwelve = ((shortenedYear - remainder) / 12)

        runningNumber += dividedByTwelve

        //print("add the amount of 12’s to get to your year" , runningNumber)

        var testNumber2 = runningNumber

        while testNumber2 > 7 {
            runningNumber -= 7
            testNumber2 -= 7
        }

        //print("if the previous number was over 7, we looped down by 7 to get " , runningNumber)

        **//if remainder == 0{
        let doomsdayPerMonth: [Int:Int] = [ 1:31, 2:28, 3:7, 4:4, 5:9, 6:6, 7:11, 8:8, 9:5, 10:10, 11:7, 12:12]

        //}
        //else{
        //let doomsdayPerMonth: [Int:Int] = [ 1:25, 2:29, 3:7, 4:4, 5:9, 6:6, 7:11, 8:8, 9:5, 10:10, 11:7, 12:12]
        //}**
        let doomsdayOfMonth = doomsdayPerMonth[month]

        var daysUntilBDay = day - doomsdayOfMonth!

        while daysUntilBDay < 0 {
            daysUntilBDay += 7
        }

        runningNumber += daysUntilBDay % 7

        //print("since the day of the month is \(day), looping down by seven would be \(daysUntilBDay % 7). Add that to above to get \(runningNumber).")

        runningNumber = runningNumber % 7

        //print(runningNumber)

        let days: [Int:String] = [0:"Wednesday", 1:"Thursday", 2:"Friday", 3:"Saturday", 4:"Sunday", 5:"Monday", 6:"Tuesday"]

        let months: [Int:String] = [1: "January", 2: "February", 3: "March", 4: "April", 5: "May", 6: "june", 7: "July", 8: "August", 9: "September", 10: "October", 11: "November", 12: "December"]

        let dayPicker = days[runningNumber]

        return ("\(months[month]!) \(day), \(year) was a \(dayPicker!).")  
    }

    func writeInWords(_ month:Int, _ day:Int, _ year:Int) -> String {
        let month1: [Int:String] = [1: "January", 2: "February", 3: "March", 4: "April", 5: "May", 6: "June", 7: "july", 8: "August", 9: "September", 10: "October", 11: "November", 12: "December"]

        let monthName = month1[month]
        return ("\(monthName!) \(day), \(year)")
    }
}

let personBday = Birthday()
print (personBday.findDayOfWeek(3,24,1914))
//print(personBday.writeInWords(4,27,1988))

Do you realize that you can get the weekday of any date in about 4 lines of code using Calendar and DateComponents. — rmaddy
– rmaddy, Commented Jan 28, 2018 at 1:17
I figured that there is probably already a code for that but this was to test my knowledge of programming. I’d be happy to learn about that though. — JWIDROFF
– JWIDROFF, Commented Jan 28, 2018 at 1:21
It looks like you need to consider variable scope. If you declare a variable inside of an if statement - be it straight or using if let, it's scope is lost once outside of the if. However, if you declare it outside of the ifthe scope is broader. *There's much more to this subject, but that's the "TL;DR" of your question. In your specific code? Move the declaration of doomsdayPerMonth outside of the if - it can be declared in several ways, from an optional, a var not known until runtime, or an "empty" dictionary. Then you need to populate it as desired inside the if. — user7014451
– user7014451, Commented Jan 28, 2018 at 1:46

rmaddy · Accepted Answer · 2018-01-28 01:39:58Z

Your commented code needs to be written as:

let doomsdayPerMonth: [Int:Int]
if remainder == 0 {
    doomsdayPerMonth = [ 1:31, 2:28, 3:7, 4:4, 5:9, 6:6, 7:11, 8:8, 9:5, 10:10, 11:7, 12:12]
} else {
    doomsdayPerMonth = [ 1:25, 2:29, 3:7, 4:4, 5:9, 6:6, 7:11, 8:8, 9:5, 10:10, 11:7, 12:12]
}

The problem with your version is that you declare local variables that have no scope outside of the if/else statement.

Please not that your entire weekday finding method can be written as:

func findDayOfWeek(_ month: Int, _ day: Int, _ year: Int) -> String {
    let date = Calendar.current.date(from: DateComponents(year: year, month: month, day: day))!
    let weekday = Calendar.current.component(.weekday, from: date)
    let formatter = DateFormatter()

    return formatter.weekdaySymbols[weekday - 1]
}

And here's your whole class with some rework. No need to hardcode month and weekday names.

class Birthday {
    let formatter: DateFormatter = {
        let fmt = DateFormatter()
        fmt.dateStyle = .long
        fmt.timeStyle = .none

        return fmt
    }()

    func dayOfWeek(_ month: Int, _ day: Int, _ year: Int) -> String {
        let date = Calendar.current.date(from: DateComponents(year: year, month: month, day: day))!
        let weekday = Calendar.current.component(.weekday, from: date)

        return formatter.weekdaySymbols[weekday - 1]
    }

    func writeInWords(_ month: Int, _ day: Int, _ year: Int) -> String {
        let date = Calendar.current.date(from: DateComponents(year: year, month: month, day: day))!

        return formatter.string(from: date)
    }
}

let bd = Birthday()
print(bd.dayOfWeek(3, 24, 1914))
print(bd.writeInWords(1, 27, 2018))

Output:

Tuesday
January 27, 2018

Giuseppe Lanza · Accepted Answer · 2018-01-28 02:22:54Z

0

Since you asked for advices here are my two cents: First, the class Birthday might contain the variables for a specific birthday, such as

class Birthday {
    let month: Int
    let day: Int
    let year: Int
}

This way the instance method would be with no parameters. The method you wrote is self sufficient and do not need an instance to work, so if you want to keep it this way I would make it static as it can compute any birthday day.

class Birthday {
    func findDayOfWeek(_ month:Int, _ day:Int, _ year:Int) -> String{

Code style is quite important for many dev teams. I would suggest you to follow this code style guide. With these indications your method would become

    func findDayOfWeek(forMonth month: Int, day: Int, ofTheYear year: Int) -> String {

What we did here is to give a clear indication of what the parameters represents when the method invocation is performed. it would be otherwise very confusing after a couple of months to see an invocation like finDayOfWeek(7, 24, 1986) especially who didn't write the method will find not intuitive which numbers represents what. findDatyOfWeek(forMonth: 7, day: 24, ofTheYear: 1986) is much more clearer.

        var runningNumber = 0

        //print( "start with " , runningNumber)

        let shortenedYear = (year - 1900)
        let remainder = shortenedYear % 12

        runningNumber += remainder

Try to initialise variables as close as possible to their usage. In this case instead of initialising runningNumber to zero at the beginning of the method you could have initialised directly with the value of remainder in this last line.

        //print("add the remainder" , runningNumber)    

        var testNumber = runningNumber

        while testNumber > 3 {
            runningNumber += 1
            testNumber -= 4
        }

        //print("because we added one for every four" ,runningNumber)

        let dividedByTwelve = ((shortenedYear - remainder) / 12)

        runningNumber += dividedByTwelve

        //print("add the amount of 12’s to get to your year" , runningNumber)

        var testNumber2 = runningNumber

testNumber finished its purpose earlier in the function. You could reuse it here.

        while testNumber2 > 7 {
            runningNumber -= 7
            testNumber2 -= 7
        }

        //print("if the previous number was over 7, we looped down by 7 to get " , runningNumber)

        **//if remainder == 0{
        let doomsdayPerMonth: [Int:Int] = [ 1:31, 2:28, 3:7, 4:4, 5:9, 6:6, 7:11, 8:8, 9:5, 10:10, 11:7, 12:12]

        //}
        //else{
        //let doomsdayPerMonth: [Int:Int] = [ 1:25, 2:29, 3:7, 4:4, 5:9, 6:6, 7:11, 8:8, 9:5, 10:10, 11:7, 12:12]
        //}**

Just like others said, here the problem was the declaration of a local variable within a scope. But again, code style and code readability is important. So careful with spaces and dictionaries with literals. Also, the two dictionaries are exactly the same except for the first two items. I would refactor this code with:

        var doomsdayPerMonth = [1: 31, 2: 28, 3: 7, 4: 4, 5: 9, 6: 6, 7: 11, 8: 8, 9: 5, 10: 10, 11: 7, 12: 12]
        if remainder != 0 {
            doomsdayPerMonth[1] = 25
            doomsdayPerMonth[1] = 29
        }

Also, since the keys are Integers I would have used an array and not dictionary, so the whole thing would look like that:

        var doomsdayPerMonth = [31, 28, 7, 4, 9, 6, 11, 8, 5, 10, 7, 12]
        if remainder != 0 {
            doomsdayPerMonth[1] = 25
            doomsdayPerMonth[1] = 29
        }

The rest of the code can be refactored accordingly to the previous suggestions.

answered Jan 28, 2018 at 2:22

Giuseppe Lanza

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8 Comments

JWIDROFF Over a year ago

Wow very very helpful!! I really appreciate it! What would you suggest on using enums for the arguments? I obviously wouldn’t want someone ever using a 32 for the day of the month or 13 for the month etc. thanks in advance!

Giuseppe Lanza Over a year ago

As I said I would not pass parameters to the function but I would use variables in the Birthday class. The initialiser can take an NSDate and out of this NSDate you can compute month day and year so that you are sure that they are always valid.

JWIDROFF Over a year ago

Can you explain why you wouldn’t pass parameters into the function and if there ever is a time that you would use parameters?

Giuseppe Lanza Over a year ago

Because if you construct the birthday class the way I said those parameters are properties of the instance already. You pass parameter to tell your instance something it doesn't know already. So the advice to not pass parameters is dependant on the fact that birthday has day month and year properties.

JWIDROFF Over a year ago

I understand what you’re saying now. So if my app had 3 textfields and a label and the label printed the input from the 3 textfields (day, month and year), would it be correct to first introduce them outside of the class let “month = UITextField.text” and then say “let self.month = month” inside of the class? (Sorry if there are problems wrong with my examples, I’m not near a computer at the moment to see if I’d get any errors from the examples I just gave you - but thanks for being patient with me!)

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