Lab 6.1: Arrays in Kotlin

In this lab you are going to experiment with Arrays. You will need to use IntelliJ IDE.

1. Create a new project and Select Kotlin and tick the Sample Code check box.

2. Modify the Main.kt content so it looks like:

   Code

   fun main(args: Array<String>) {
   
   } 
   

3. Inside the main(..){...} we are going to declare and initialise three arrays, intArray, stringArray, and doubleArray:

   Code

   fun main(args: Array<String>) {
       val intArray = intArrayOf(1, 2, 3, 4, 5)
       val stringArray = arrayOf("apple", "banana", "cherry", "date", "elderberry")
       val doubleArray = DoubleArray(5) // An array of doubles with a size of 5
   }
   

4. To output these arrays we are going to use joinToString()

   Code

   println("intArray: ${intArray.joinToString()}")
   println("stringArray: ${stringArray.joinToString()}")
   println("doubleArray: ${doubleArray.joinToString()}")
   

   • The joinToString() function is used to convert arrays into strings for display.

   Output

   intArray: 1, 2, 3, 4, 5
   stringArray: apple, banana, cherry, date, elderberry
   doubleArray: 0.0, 0.0, 0.0, 0.0, 0.0
   

5. Now let's access the first and second index of intArray and stringArray respectively. Add the following underneath the last block of code:

   Code

   println("First element of intArray: ${intArray[0]}")
   println("Second element of stringArray: ${stringArray[1]}")
   

   • Remember the array[index] points to the position of a value whose index starts from 0 to size of the array - 1.

   Output

   First element of intArray: 1
   Second element of stringArray: banana
   

   • Try and get the last element from both arrays.

6. We can iterate of an array using a for loop. Continuing underneath the last code added:

   Code

   println("Iterating through intArray, using object:")
   for (element in intArray) {
       println(element)
   }
   

   Output

   Iterating through intArray, using object:
   1
   2
   3
   4
   5
   

   • the element is like an object in a toy box.

7. Continuing with looping we can setup the for loop differently, repeat:

   Code

   println("Iterating through stringArray, using indexing:")
   for (i in 1..stringArray.lastIndex) {
           println(stringArray[i])
       }
   

   Output

   Iterating through stringArray, using indexing:
   banana
   cherry
   date
   elderberry
   

8. We can modify and array when the array is mutable as in it is a var not a val. Modify the third element of intArray by setting it to 10 and then print the modified intArray:

   Code

    intArray[2] = 10
    println("Modified intArray: ${intArray.joinToString()}")
   

   Output

   Modified intArray: 1, 2, 10, 4, 5
   

9. We create a two-dimensional array (twoDArray) and populate it with values. We then iterate through the two-dimensional array and print its contents.

   Info

   • a 2D array is like a matrix/table

     a	b
     1	2
     3	4

   Code

   val twoDArray = Array(3) { IntArray(4) } // 3x4 matrix
   for (i in 0 until 3) {
       for (j in 0 until 4) {
           twoDArray[i][j] = i + j
       }
   }
   

   Output

   Two-dimensional array:
   0, 1, 2, 3
   1, 2, 3, 4
   2, 3, 4, 5
   

10. Now define a custom data class Person and create an array of Person objects (personArray). We iterate through personArray and print the name and age of each person:

    Code

    data class Person(val name: String, val age: Int)
    val personArray = arrayOf(
        Person("Aiya", 28),
        Person("Bobi", 22),
        Person("Charlie", 35)
    )
    
    println("Array of Persons:")
    for (person in personArray) {
        println("Name: ${person.name}, Age: ${person.age}")
    }
    

    Output

    Output

    Array of Persons:
    Name: Aiya, Age: 28
    Name: Bobi, Age: 22
    Name: Charlie, Age: 35