Iterating in Arrays

Whenever you want to process certain or all elements of an array or fill the array with elements, loops are always there to help you. Instead of dealing with each element manually one by one and writing tons of lines of code, especially for large arrays, you can simply use a for loop.

Iterating Over Indices

The first approach to iterate over an array is to iterate over its indices. Remember the length property of an array? We'll make use of it here. Let's first take a look at the for loop with until:

Main


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object Main {
  def main(args: Array[String]): Unit = {
    var charArray = Array('a', 'b', 'c', 'd', 'e')
    for (i <- 0 until charArray.length) {
      println(charArray(i))
    }
  }
}

We just print all the elements of the array of Char elements one by one by iterating over the indices of this array. Our loop variable i starts from 0 to the length of the array exclusive, or to the length - 1 inclusive which is the index of the last element.

Let's now take a look the same example, but instead of until we'll useto:

Main


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object Main {
  def main(args: Array[String]): Unit = {
    var charArray = Array('a', 'b', 'c', 'd', 'e')
    for (i <- 0 to charArray.length - 1) {
      println(charArray(i))
    }
  }
}

Since to includes the end value, we use length - 1 here which is index of the last element.

Iterating Over Elements

As we have mentioned previously, a for loop also allows to iterate over elements in a collection. So its range becomes simply the array over the elements of which we want to iterate.

Let's modify our previous example to illustrate this:

Main


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object Main {
  def main(args: Array[String]): Unit = {
    var charArray = Array('a', 'b', 'c', 'd', 'e')
    for (element <- charArray) {
      println(element)
    }
  }
}

Here, at each iteration the value of the current element is assigned to our element variable. This approach is often a preferred one than the two above.

Moreover, we can iterate over the indices of the array in a more concise way by accessing the array indices using the indices property:

Main


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object Main {
  def main(args: Array[String]): Unit = {
    var charArray = Array('a', 'b', 'c', 'd', 'e')
    for (i <- charArray.indices) {
      charArray(i) = (charArray(i) + 1).toChar
      println(charArray(i))
    }
  }
}

In this example, we add 1 to the encoding of each Char of our array and convert the resulting encoding back to Char. In a way, we simply shift each letter by one to the right. Once again, Iterating over the elements directly wouldn't allow us to change the elements and raise an error.

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Seção 4. Capítulo 2