Using a for-in loop with a switch statement

@ Steve Hunter Thanks for looking at that code. Someone pointed that out to me a a little earlier. I haven't had a chance to enter it yet. I switched over to Objective C, and I started working at midnight now its 7 am I need to get some rest soon. Thanks

@Steve, thanks for the answer. I see where I made the mistake of thinking the for-in loop would iterate through by index instead of value. One quick question, why did you need the 'else'? The 'if' combined with the 'switch' contains all the possible outcomes.

@Hans, thanks for looking at my question :)

The if and switch don't capture all the possible outcomes - that's why the else is there.

Work it through - you're dealing with a user-input function here - the user uses your function in their app a bit wrong and enters dayType("tomorrow");. What happens?

The switch case is never reached; the string day is never equal to a member of the array at any index. So, the function would skip the if and reach the return, returning a wholly unhelpful empty string as a legacy of its initialisation, rather than any text. So, I use an else to capture the scenario that the user may enter a mistyped day, or a nonsense string. In the alternative, you could initialise the string to something like "Not a day" but that isn't quite as clear. My preference, I guess.

It is, as you say, about handling all eventualities. When your code accepts parameters it is dangerous to assume that the right parameters will be passed in so having code that is verbose in its output helps pin down the route the code is taking. Outputting blank strings or nulls can be hugely confusing! Here, if you get a "Not a day" output, you know why. Swift insists on the default statement although, in this example, that is impossible to reach. The else is very easy to get to, though.

I hope that makes sense.

Steve.

ahhhhhh, I see your point with misspellings and foreseeing all possible outcomes, but wouldn't the default be triggered "Unlikely to be a day"? It seems the default would take care of that.

No - the switch case is only reached if the parameter entered equals one of the elements of the array.

The default is never reached in the current guise - all the case statements cover all positive if outcomes. The default: would only be reached if I forgot to implement all the outcomes 0 ... 6.

Make sense?

I ran it, your right, no matter what I type in I can't trigger the default statement. Even after I remove the else. As you said earlier the Swift language requires it. Just seems odd I can't get to it in this scenario.

Thank you very much for your help and very fast answers! :-)

It isn't odd, no.

The default is triggered when none of the case tests match what is passed to the switch in the current iteration. In our example, we have a totally closed and controlled switch - we gain control with the day == daysOfWeek[i] as we only progress into the switch when we have a direct match, a true boolean outcome. We have validated the parameter passed in.

The array is fixed with 7 elements - that is immutable. The switch has all seven outcomes handled - each array element, 0 to 6, have a case representing them. So, it is impossible for the default to be triggered.

If we approached this from where you started this and switch on the value passed into the function and try matching that to the array elements, then the default would handle the erroneous entries as we don't validate the entry outside of the switch. It would be ugly code but:

func daySwitch(day: String) -> String {
    switch day {
        case "Monday",
             "Tuesday",
             "Wednesday",
             "Thursday",
             "Friday": return "Weekday"
        case "Saturday",
             "Sunday": return "Weekend"
        default: return "Not a day"
    }
}

This negates the need to declare your array completely but covers all eventualities and uses default to pick up the pieces of any mistakes. It remains, however, inelegant code.

Hope that all makes sense!

Steve.

I understand now. In the example when you used the for-loop, the switch is contained inside the for-loop's block of code, since it iterates through the array using the index # (daysOfWeek[i]), if the user enters a parameter that doesn't match a value in the array, the for-loop kicks over to the else because it doesn't see the default (because it has no index # association it's invisible to the for-loop). Basically the for-loop is in control of the switch and the default doesn't have a index #. I get that.

In the example you just wrote the the switch is in control and if the user doesn't enter a matching value the default does trigger because it's like like the for-loops else.

correct?

Thank you very much!!! :-)

No problem! Glad to have helped!

Steve.

Steve, one more question. Answer whenever you can. I redid the code using an integer for the argument and this time using the for-in loop (I understand it goes through by value), but when i create a variable to hold my function, no matter what # I put inside the argument, I get the same exact string "It's a weekday":

let daysOfWeek = [1, 2, 3, 4, 5, 6, 7]

func weekdayOrWeekend(day: Int) -> String? {

    for day in daysOfWeek{

        switch day{
        case 1...5:
            return "It's a weekday"
        case 6,7:
            return "It's a weekend"
        default:
            return "Not a valid day"
        }
    }
    return nil
}

//variable with function
var randomDay = weekdayOrWeekend(15)

I have to look your notes over more intently. See I understand loops and conditionals, but using them in the right context seems to be my problem. When to use a 'for' vs a 'for-in' and an 'if-else' vs a 'switch' and combining then them -or not- is where it gets tricky. The first question you answered for me I understand 100%. For this example I do see your point in saying the for-in loop is pointless as the switch statement accomplishes the same exact task. I see why your saying the array is pointless for days of the week but if it were something such as school test scores I would think you would need to give the user something to reference from eg. let grades = [0...60, 61...69, 70...80, 81...90, 91...100] and using a switch would easily give grade scores F-A as instead of looping through the grades.

It makes sense to write the problem out first and then try to find the easiest way to solve it. I was at the beginning of the Enum track and wanted to try to accomplish this without using Enums.

I'll try to get it down packed and send you a message later. Thanks again!

This is something I came up with in the shower just now. I'm not sure if it's exactly what you were describing but it let's you input a student's name and associates that name with whatever score and grade you enter.

func studentNameAndGrade(#studentName: String, #studentGrade: Int) -> String{

    var student = studentName
    var score = studentGrade

    switch studentGrade {
    case 0...59:
        return "\(student)'s score is: \(score) and grade is a F"
    case 60...70:
        return "\(student)'s score is: \(score) and grade is a D"
    case 71...80:
        return "\(student)'s score is: \(score) and grade is a C"
    case 81...90:
        return "\(student)'s score is: \(score) and grade is a B"
    case 91...100:
        return "\(student)'s score is: \(score) and grade is an A"
    default:
        return "Invalid score please re-enter a score between 0-100"

    }

}

var sample = studentNameAndGrade(studentName: "Rael", studentGrade: 99)
sample

Your absolutely right. I was thinking about it earlier. Thank very much for your help. I'm sure I'm going to have many more questions.

Talk to you soon!

✌✌