For loop over collections in Kotlin - Step-by-Step Execution

Concept Flow - For loop over collections

Start

↓

Get collection

↓

Take first element

↓

Execute loop body with element

↓

More elements?

No→End

Yes↓

Take next element

The loop starts by getting the collection, then takes each element one by one, runs the loop body, and repeats until no elements remain.

Execution Sample

Kotlin

val fruits = listOf("apple", "banana", "cherry")
for (fruit in fruits) {
    println(fruit)
}

This code loops over a list of fruits and prints each fruit.

Execution Table

Iteration	fruit value	Action	Output
1	"apple"	Print fruit	apple
2	"banana"	Print fruit	banana
3	"cherry"	Print fruit	cherry
-	-	No more elements, loop ends	-

💡 All elements in the collection have been processed, loop ends.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
fruit	undefined	"apple"	"banana"	"cherry"	undefined

Key Moments - 2 Insights

Why does the variable 'fruit' change each iteration?

Because in each iteration, 'fruit' takes the next element from the collection, as shown in execution_table rows 1 to 3.

What happens when the loop reaches the last element?

After printing the last element, the loop checks for more elements, finds none, and ends (see last row in execution_table).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'fruit' in iteration 2?

A "apple"

B "banana"

C "cherry"

D undefined

💡 Hint

Check the 'fruit value' column in the second row of execution_table.

At which iteration does the loop stop running?

A After iteration 3

B After iteration 1

C After iteration 2

D It never stops

💡 Hint

Look at the exit_note and the last row of execution_table.

If the collection had 4 elements, how would the execution_table change?

A The output would be empty

B The loop would stop after 3 iterations anyway

C There would be 4 iterations with fruit values for each element

D The loop would run infinitely

💡 Hint

Refer to how each element corresponds to one iteration in execution_table.

Concept Snapshot

For loop over collections in Kotlin:
for (item in collection) {
    // use item
}
Loops through each element in the collection one by one.
The loop variable takes each element in order.
Loop ends when all elements are processed.

Full Transcript

This visual execution shows how a Kotlin for loop works over a collection. The loop starts by getting the collection and then takes each element one by one. In each iteration, the loop variable 'fruit' holds the current element. The loop body prints the fruit. After the last element is processed, the loop ends. The variable tracker shows how 'fruit' changes each iteration. Key moments clarify why 'fruit' changes and when the loop stops. The quiz tests understanding of variable values and loop termination.