How do I change the values of an array using a for-in loop inside a function or a nested function?

Question

Running through the swift 2.0 documentation and Im trying to practice some stuff I learned in c++. One of which is the ability to modify array elements inside of my element which I am having trouble doing in swift.

 var scoreOfStudents = [86, 93, 68, 78, 66, 87, 80]

 func returnScoresWithCurve (inout scoresOfClass : [Int]) -> [Int] {
      for var score in scoresOfClass {
          if score < 80 {
              score += 5
          }
      }
      return scoresOfClass
 }

Don't know what my error is because in the for-in loop, the scores less than 80 are being added but aren't being modified in the array I passed. Also would like to know how I can do this same thing using a nested function and not for-in loops.

Nikita Kukushkin · Accepted Answer · 2015-07-27 00:38:56Z

21

I believe that using a for-in loop like this, your score variable is value copy of the array element, as opposed to a reference variable to the actual index of your array. I would iterate through the indices and modify scoresOfClass[index].

This should do what you're looking to do.

var scoreOfStudents = [86, 93, 68, 78, 66, 87, 80]

func returnScoresWithCurve(inout scoresOfClass: [Int]) -> [Int] {
    for index in scoresOfClass.indices {
        if scoresOfClass[index] < 80 {
            scoresOfClass[index] += 5
        }
    }
    return scoresOfClass
}

Also, why are you you using inout scoresOfClass when you're returning?

edited Jul 27, 2015 at 0:38

Nikita Kukushkin

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answered Jul 26, 2015 at 23:16

schrismartin

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3 Comments

Nikita Kukushkin Over a year ago

Use ..< instead of -1.

Nikita Kukushkin Over a year ago

Or even better: for index in scoresOfClass.indices.

Muhammad Over a year ago

thanks! this worked but @Mario Zannone 's solution is much more simple and cleaner

Mario Zannone · Accepted Answer · 2015-07-26 23:27:36Z

13

@ChrisMartin is correct: changing score you are simply changing a copy of the value, not the original in the array, and the approach with the index will work.

Another, more swifty solution is the following:

func returnScoresWithCurve (scoresOfClass : [Int]) -> [Int] {
    return scoresOfClass.map { $0 < 80 ? $0 + 5 : $0 }
}

Here returnScoresWithCurve will return a modified array instead of changing the original. In my view this is a plus.

answered Jul 26, 2015 at 23:27

Mario Zannone

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2 Comments

Muhammad Over a year ago

talking about code cleanliness, Thanks for the nice answer! Now Im on to figure out how I can use a nested function and do this problem

CalZone Over a year ago

Better answer than the loopy one.

mahega · Accepted Answer · 2019-07-22 15:52:48Z

0

Another IMO beautiful solution in Swift:

 var scoreOfStudents = [86, 93, 68, 78, 66, 87, 80]

 func returnScoresWithCurve (inout scoresOfClass : [Int]) -> [Int] {
      for (index, score) in scoresOfClass.enumerated() {
          if score < 80 {
              scoresOfClass[index] = score + 5
          }
      }
      return scoresOfClass
 }

answered Jul 22, 2019 at 15:52

mahega

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