Loops allows you to repeat a set of instructions multiple times.
For and While Loops
[object Object]
Syntax of For Loops
Loop using a collection
for ([temporary_name] in [collection_name]) {
}
Loop using a specific Range
for ( [temporary_name] in [start]..[end] ) {
}
for ( [temporary_name] in [start] downTo [end] step [amount_to_increment]) {
}
for ( [temporary_name] in [collection_name].indices() ) {
}
Examples
Iterating through an array of integers.
val lotteryNumbers = arrayOf<Int>(32, 6, 20, 1, 7);
for(number in lotteryNumbers) {
println(number)
}
Looping using a range
for(number in 1..5) {
println(number)
}
In the example, the loop will iterate 5 times and print 1, 2, 3, 4, and 5.
Loop using until and downTo
for(number in 1 until 10 step 2) {
}
for(number in 10 downTo 0 step 2) {
}
In the above examples - the first - starts from 1 and goes until 10. Each iteration, the counter will be increase by 2 every time because of [step 2]. It will start at 1, then 3, then 5, then 7, then 9.
If step were 3, the counter will be increased by 3 after each iteration.
In the second example above, it is the opposite. It starts from 10 and goes down to 0 with a step of 2. 10 > 8 > 6 > 4 > 2 > 0.
Loop using Array length
val lotteryNumbers = arrayOf<Int>(32, 6, 20, 1, 7)
for(number in lotteryNumbers.indices) {
}
In the example, the loop will iteration 5 times since indices returns the length of the array - (5).
The value of number will be 0, 1, 2, 3, and 4.
While Loops
While Loops are a different form of loop in Kotlin. Unlike the For Loop which repeats a set of instructions for a specific range, while loops repeats a set of instructions until a specific condition is false. They are used when you do not know the amount of iterations to complete a specific task.
Syntax for While Loops
while ([condition]) {
...
}
do {
...
} while ([condition])
The 2 type of while loops shown is the regular while loop (first) and the do-while loop (second).
The difference between the two is that the do-while loop will execute the instructions in the curly brackets - { } - at least once before checking if the condition is true/false.
Examples for While Loops
var playerIsAlive = true;
while(playerIsAlive) {
// Code to repeat here
}
The above example is a simple while loop that will keep on going while the playerIsAlive boolean is true. It will not stop until playerIsAlive is set to false.
var x = 0;
do {
println("Executed!")
} while (x > 0)
For this do-while loop example, it demonstrates the difference between the normal while loop and itself. Even though the condition for when the loop will continue is when x is greater than 0, the loop will still execute the code in the curly brackets once since it checks the condition afterwards.
