When without argument in Kotlin - Step-by-Step Execution

Concept Flow - When without argument

Start

↓

Evaluate conditions one by one

↓

If condition true?

No→Check next condition

Yes↓

Execute corresponding block

↓

Exit when block executed

↓

End

The 'when' without argument checks each condition in order and runs the block for the first true condition, then stops.

Execution Sample

Kotlin

val x = 15
when {
  x < 10 -> println("Less than 10")
  x in 10..20 -> println("Between 10 and 20")
  else -> println("More than 20")
}

This code checks x against conditions without an argument and prints the matching message.

Execution Table

Step	Condition Checked	Condition Result	Action Taken	Output
1	x < 10	false	Check next condition
2	x in 10..20	true	Execute block	Between 10 and 20
3	Exit	N/A	Stop checking further

💡 Condition 'x in 10..20' is true, so execution stops after this block.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	15	15	15	15

Key Moments - 2 Insights

Why does the 'when' stop after the second condition even though there is an 'else'?

Because the second condition 'x in 10..20' is true, the corresponding block runs and 'when' exits immediately without checking 'else' (see execution_table row 2 and 3).

What happens if none of the conditions are true and there is no 'else'?

The 'when' expression does nothing and no block runs, because it only executes the first true condition block (not shown in this example but implied by the flow).

Visual Quiz - 3 Questions

Look at the execution table, what is the result of checking 'x < 10' at step 1?

A true

B false

C error

D not evaluated

💡 Hint

Check the 'Condition Result' column at step 1 in the execution_table.

At which step does the 'when' expression stop checking conditions?

A Step 1

B Step 3

C Step 2

D It never stops

💡 Hint

Look at the 'Action Taken' and 'Exit' rows in the execution_table.

If x was 25, which output would appear according to the execution flow?

A More than 20

B Between 10 and 20

C Less than 10

D No output

💡 Hint

Think about which condition would be true if x=25, based on the conditions in the code sample.

Concept Snapshot

when without argument:
- Checks each condition in order
- Executes block for first true condition
- Stops after executing one block
- 'else' acts as default if no conditions true
- Useful for complex condition checks without a single value

Full Transcript

The Kotlin 'when' expression without an argument works by checking each condition one by one. It runs the block for the first condition that is true and then stops checking further. For example, if x is 15, it first checks if x < 10, which is false, then checks if x is between 10 and 20, which is true, so it prints 'Between 10 and 20' and stops. If none of the conditions are true and there is an 'else' block, it runs that as a default. This makes 'when' without argument a flexible way to handle multiple conditions clearly and simply.