Kotlin Basic Syntax: Loop and Conditional Control Operator

In this article, we will cover some basic syntax of Kotlin. Like for, dowhile and while loop, if and when control operator, downTo, step, in and its use. These are first and the very basic concept of any programming language.

Using the if control operator in Kotlin

If the conditional operator in Kotlin is similar to the java and it can be used in the same as like into the java only difference as normal is that we don't require ";"  operator at the end of every line.

var a=11
    var b=20
    if(a < b){
        println("$a is less then $b" )
    }

Output:-

11 is less then 20

Using the if with else control operator in Kotlin

we can use the traditional if else statement like we use in the java and syntax for this as given below.

println("Enter the number:")
    var c = readLine()

    var a=c!!.toInt()
    var b=20
    if(a < b){
        println("$a is less then $b" )
    }
    else{
        println("$a is greater then $b")
    }

Output:

Enter the number:12
12 is less then 20

Enter the number:21
21 is greater then 20

Using if else like an expression

We can use the if else control statement like an expression.

println("Enter Two Number\b:")
    var (a,b) = readLine()!!.split(' ')
    var n1:Int=a.toInt()
    var n2:Int=b.toInt()

    var maxvalue:Int= if(n1>n2) n1 else n2

    println("$maxvalue is the Max value from $n1 and $n2")

Output:

Enter Two Number:
45 12
45 is the Max value from 45 and 12

Using case, Switch and when operator into Kotlin

The case is not supported by the Kotlin instead of the case operator we have when statement which does the work like case statement of c language. It will work like switch operator of the Java.

println("Enter a Number from 0 to 9:")
    var number= readLine()
    when(number!!.toInt()){
        0 -> print("You have entered: Zero")
        1 -> print("You have entered: One")
        2 -> print("You have entered: Two")
        3 -> print("You have entered: Three")
        4 -> print("You have entered: Four")
        5 -> print("You have entered: Five")
        6 -> print("You have entered: Six")
        7 -> print("You have entered: Seven")
        8 -> print("You have entered: Eight")
        9 -> print("You have entered: Nine")
        else -> print("${number.toInt() } is out of Range")
    }

Output:

Enter a Number from 0 to 9:
0
You have entered: Zero

Using "in" operator in Kotlin for checking the value from the range

we can use the "in" operator where we have to validate the number from the range. For example, we have to check whether the given number follow between 1 to 10;

println("Enter a Number for validation:")
    var number= readLine()!!.toInt()
    if (number in 1..10){
        println("$number is within range")
    }
    else{
        println("$number is out of range")
    }

Output:
run one with the input value 5

Enter a Number for validation:
5
5 is within range

run two with the input value 11

Enter a Number for validation:
11
11 is out of range

You can see the example that range validation can be done very easily in Kotlin. In other languages, we have to do iteration using for loop but in Kotlin, we can do it by just using the if and in the operator.

Using !in operator to validate the range

println("Enter the index of List:")
    var number= readLine()!!.toInt()
    var list:List<String> = listOf("Apple","Bananana","Orange")
    if (number !in 0..list.lastIndex){
       println("$number is out of Index")
    }
    else{
        println("${list.get(number)} is at Index $number")
    }

Output

Run1
Enter the index of List:
0
Apple is at Index 0
Run2
Enter the index of List:
-1
-1 is out of Index

Using for loop in Kotlin

There are many ways to use the for loop into the Kotlin, below is the some of the use case and syntax of for loop.

for loop iterates through all type which provides iterator.

A very simple for loop in Kotlin.

for(i in 1..5){
        println("$i")
    }

Using downTo and Step Operator in Kotlin with for loop

We use the for loop to iterate from some start value to some up value. In Java when we have to do the reverse iteration then we use I-- operator and start the value from the higher value to lower and value and vice versa.  Unlike Java in Kotlin, we have downTo operator using which we can iterator in reverse order.

for(i in 9 downTo 0 ){
            print("$i")
    }

When we run the above code we will get the below output.

9876543210

i.e. the loop will iterate from 9 to 0 and print all the integer 9 8 7  up to 0, but what if we want to print the number like 9 7 5 3 1 only. If we required printing the output like that then we have to use the step operator.

for(i in 9 downTo 0 step 2){
            print("$i")
    }

Output:

97531
Process finished with exit code 0

Using for loop with List or array in Kotlin

Iterating with the index of the List.

val list:List<String> =listOf("a","b","c","d")
    for (item in list.indices){
        print("${list[item]},")
    }

Output:

a,b,c,d,
Process finished with exit code 0

or if you want to use the item instead of the index then it is more simple than any other programming language.

val list:List<String> =listOf("a","b","c","d")
    for(item in list){
        print("$item,")
    }

The output of the above code will same as previous code only the implementation part are changed.

a,b,c,d,
Process finished with exit code 0

While loop in Kotlin

The syntax of while and dowhile was same as the java there is no any change in that.

val list:List<String> =listOf("a","b","c","d")
    var x=0
    while (x<list.size ){
        println("is ${list[x]} at Index $x")
        x++
    }

When we run the above code we will get the following output.

a at Index 0 
b at Index 1 
c at Index 2 
d at Index 3 

Similarly, we can use the do while loop in Kotlin.

val list:List<String> =listOf("a","b","c","d")

    var x=0
    do{
        println("${list[x]} at Index $x" )
        x++
    }while (x<list.size)

Output:

a at Index 0
b at Index 1
c at Index 2
d at Index 3

Conclusion

In this article, we have tried to present the basic syntax of the Kotlin programming. We can say these are building block if you what to be a good Kotlin developer. We have tried to make all the example as simple as possible but still, if you have any doubt or query you can put your comment below.