Kotlin basics : Looping mechanisms

Contants
While Loop
doWhile Loop
For Loop
Using BREAK and CONTINUE in looping
Using custom label for the loop
Usage of when construct

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While Loop

• We use this construct to execute iterate a collection of elements until a condition is met
• We use the while looop when we are not sure how many loops are needed until a condition is met
• Thus we set a condition

 private fun initiate() {
        // List of cities
        var cityList = listOf("Bangalore","Delhi","Chennai","Calcutta")
        executeWhileLoop(cityList)
    }

    private fun executeWhileLoop(cityList: List<String>) {
        var i=0
        while (i<cityList.size-1){
            println(cityList[i])
            i++
        }
}

---

doWhile Loop

• We use the doWhile loop when we are not sure how many loops are needed until a condition is met.
• Thus we set a condition
• This is the same as the do-while loop but here we execute the statements and then check the condition, which is in reverse order for doWhile loop.

 private fun initiate() {
        // List of cities
        var cityList = listOf("Bangalore","Delhi","Chennai","Calcutta")
        executeDoWhileLoop(cityList)
    }

    private fun executeDoWhileLoop(cityList: List<String>) {
        var i=0
        do {
            println(cityList[i])
            i++
        }while (i<cityList.size-1)
    }
}

---

For Loop

• We use the for a loop when we know the number of iterations we need to perform.
• We use the range for this purpose.

private fun initiate() {
        // List of cities
        var cityList = listOf("Bangalore","Delhi","Chennai","Calcutta")
        executeForLoop(cityList)
    }

    private fun executeForLoop(cityList: List<String>) {
      for (city: String in cityList){
          println(city)
      }
    }
}

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Using break and continue in looping

• continue is a keyword used to skip execution of current iteration from the line it is mentioned in the loop.
• break is a keyword used to skio execution of all left over iteration from the line it is mentioned int he loop.

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Using custom label for the loop

• We can assign a custom name as a tag for a loop and can refer to this label and use it to break the loop.
• This is very useful in multidimensional or nested looping mechanism.

private fun initiate() {
        // List of cities
        var cityList = listOf("Bangalore","Delhi","Chennai","Calcutta")
        usingLabel(cityList)
    }

    private fun usingLabel(cityList: List<String>) {
        myLabel@for (city: String in cityList){
            if (city == "Calcutta"){
               break@myLabel
            }else{
                println(city)
            }
        }
}

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Usage of when construct

• we use this when we need to evaluate multiple expressions

// STRUCTURE
when(value) {
 expression1 -> statement1
 expression2 -> statement2
 expression3 -> statement3
 else -> statement4
}