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Kotlin Tutorial - 3 Control Flow (Iteration)
In Kotlin, there are two main types to create an iteration or loop by using
while and for.In
while loop, the condition is checked first before the code inside while block is executed. This is the basic syntax of while loop.while(condition) {
// code..
}In this example, the
while loop is used to prints out the number from 1 until 4.fun main() {
var num = 1
while(num <= 4) {
println(num)
num++
}
}Output
1
2
3
4Based on the code above, the
while loop has a flow like this:while block.Notice that inside
while block, there is a code that used to increase the num value by 1 with ++ operator. The num++ equals to num = num + 1.Here it is another similiar operator that usually used together with loop mechanism.
| Operator | Description |
|---|---|
+= |
a += b equals to a = a + b
|
-= |
a -= b equals to a = a - b
|
*= |
a *= b equals to a = a * b
|
/= |
a /= b equals to a = a / b
|
%= |
a %= b equals to a = a % b
|
++ |
a++ equals to a = a + 1
|
-- |
a-- equals to a = a - 1
|
There is another type of
while loop called do while loop. The do while loop executes the code inside do while block then check the condition. This is the basic syntax of do while loop.do {
// code..
} while(condition)In this example, the
do while loop is used.fun main() {
// create variable called num
var num = 1
// use do while loop
do {
// prints out the num's value
println(num)
// increase the num's value by 1
num++
} while (num < 0)
}Output
1Based on the code above, the code inside
do while block is executed first then the condition of num value is checked.For loop is a loop mechanism that suitable for range condition. This is the basic syntax of using
for loop.for(range_condition) {
// code..
}In this example, the
for loop is used to prints out number from 1 until 4.fun main() {
for (num in 1..4) {
println(num)
}
}Output
1
2
3
4Based on the code above, the range condition is specified using
in keyword followed with specified range.Another way to create range condition is using
until keyword.var_name in initial_value until limit_valueThis is the example of using
until keyword.fun main() {
for(num in 1 until 3) {
println(num)
}
}Output
1
2Based on the code above, the
num value that printed out is 1 and 2 because the 3 acts as a limit value only. If the num value equals with the limit value (in this case is 3), the code execution inside for block is stopped.The
for loop is suitable for iterating through collection like List. In this example, the for loop is used to iterate through list.fun main() {
// create a list of integers
val list = listOf(1,2,3,4)
// using for loop
// to iterate through every list items
for(item in list) {
println(item)
}
}Output
1
2
3
4Based on the code above, the specified range is
item in list which means every item exists in list, execute the code inside for block. The code inside for block is executed to prints out the value from item temporary variable.The nested
for loop is also available. In this example, the nested for loop is used to iterate through list of collections.fun main() {
// create a list of collections
val database = listOf(
listOf("Docker","Git","Ansible"),
listOf("Kotlin","Java","Golang")
)
// using nested for loop
for (list in database) {
for (item in list) {
println(item)
}
}
}Output
Docker
Git
Ansible
Kotlin
Java
GolangBased on the code above, the inner loop is executed first then the outer loop is executed.
The
break and continue keyword usually used together with loop mechanism. The continue keyword means continue the execution of code whilst break keyword means stop the code execution.In this example, the
continue keyword is used to print out only odd values.fun main() {
for (num in 1..10) {
if (num % 2 == 0) {
continue
}
println(num)
}
}Output
1
3
5
7
9Based on the code above, the
continue keyword is used to execute into the next loop which means if num % 2 == 0 condition is true, the num value is skipped then the next loop is executed.In this example, the
break keyword is used to stop the execution inside while loop.fun main() {
var num = 1
while(true) {
if (num == 3) break
println(num)
num++
}
}Output
1
2Based on the code above, the
break keyword is used to stop the execution if the value from num variable is equals 3.I hope this article is helpful for learning the Kotlin programming language. If you have any thoughts or comments you can write in the discussion section below.
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