For Loop II in Kotlin

There is a more powerful way to use the for loop in Kotlin.

A Kotlin for loop goes through a range of values. Its loop variable takes each value of the range in turn. The general form is:

for (i in start until end) {
	instruction1
	instruction2
	...
}

Let's break down each component:

• The start value is where the loop variable begins. The variable is created by the loop itself, so there is no var or type in front of it.

• The end value is where the loop stops. With until the end value itself is not included, so the loop continues while the variable is less than end.

• After each iteration the loop variable moves on to the next value in the range, by 1 unless you add step. You never update it yourself.

Example:

for (i in 0 until 4) {
	println("Hello world!")
}

// This code prints "Hello world!" on four different lines

Let's break down this code:

• The start value is 0. The loop creates the iterator variable i and starts counting from 0.

• The end value is 4, which is excluded because we use until, meaning the loop will run as long as the iterator variable, i, is less than 4.

• After each iteration, after running the code inside {}, i moves on to the next value, which is 1 more.

This is what the computer does behind the scenes during this loop:

0. Creates and initializes a variable i = 0

1. First iteration:
	a. Is i < 4 true? <=> Is 0 < 4 true? Yes. 
	b. Run the code inside {}. Print "Hello world!".
	c. next value => i = 1
	
2. Second iteration:
	a. Is i < 4 true? <=> Is 1 < 4 true? Yes. 
	b. Run the code inside {}. Print "Hello world!".
	c. next value => i = 2
	
3. Third iteration:
	a. Is i < 4 true? <=> Is 2 < 4 true? Yes. 
	b. Run the code inside {}. Print "Hello world!".
	c. next value => i = 3
	
4. Fourth iteration:
	a. Is i < 4 true? <=> Is 3 < 4 true? Yes. 
	b. Run the code inside {}. Print "Hello world!".
	c. next value => i = 4

5. Fifth iteration:
	a. Is i < 4 true? <=> Is 4 < 4 true? No.
	b. Exit the loop.

Assignment

Let's print "I promise to learn coding." 5 times using a for loop.

Hint
Look at the examples above if you get stuck.