For-in loop with ranges in Swift - Step-by-Step Execution

Concept Flow - For-in loop with ranges

Start

↓

Set range start and end

↓

Pick next number in range

↓

Execute loop body with number

↓

More numbers in range?

No→End

Yes↓

Pick next number in range

The loop picks each number from the range one by one and runs the code inside the loop for each number until all numbers are used.

Execution Sample

Swift

for i in 1...3 {
    print(i)
}

This code prints numbers 1, 2, and 3, one on each line.

Execution Table

Iteration	i value	Action	Output
1	1	Print i	1
2	2	Print i	2
3	3	Print i	3
4	-	No more numbers in range	-

💡 i reaches 3, next number does not exist, loop ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	-	1	2	3	-

Key Moments - 2 Insights

Why does the loop stop after printing 3?

Because the range 1...3 includes only numbers 1, 2, and 3. After 3, there are no more numbers, so the loop ends as shown in execution_table row 4.

What if we use 1..<3 instead of 1...3?

The range 1..<3 includes 1 and 2 but not 3. So the loop would run only twice, printing 1 and 2. This is a half-open range.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i at iteration 2?

A 1

B 3

C 2

D -

💡 Hint

Check the 'i value' column in the execution_table at iteration 2.

At which iteration does the loop stop because there are no more numbers?

A 3

B 4

C 2

D 1

💡 Hint

Look at the 'Action' column where it says 'No more numbers in range'.

If the range changes to 1..<3, how many times will the loop run?

A 2 times

B 3 times

C 1 time

D 4 times

💡 Hint

Recall that 1..<3 excludes 3, so it includes 1 and 2 only.

Concept Snapshot

for i in start...end {
    // code using i
}

- Runs loop from start to end including end
- i takes each number in the range
- Use ... for closed range (includes end)
- Use ..< for half-open range (excludes end)

Full Transcript

This visual execution shows how a for-in loop with a range works in Swift. The loop variable i takes each number from the range 1 to 3, including 3. Each iteration prints the current value of i. The loop stops after reaching the last number in the range. The execution table tracks each iteration, the value of i, the action taken, and the output printed. The variable tracker shows how i changes over time. Key moments clarify why the loop stops and the difference between closed and half-open ranges. The quiz tests understanding of the loop variable values and loop termination conditions.