Stride for custom step in Swift - Step-by-Step Execution

Concept Flow - Stride for custom step

Start at 'from'

↓

Check: current < to?

No→EXIT

Yes↓

Execute loop body

↓

Add 'by' to current

↩Back to Check

This flow shows how stride starts from a value, checks if it is less than the end, runs the loop body, then adds the step size before repeating.

Execution Sample

Swift

for i in stride(from: 0, to: 10, by: 3) {
    print(i)
}

This code prints numbers from 0 up to (but not including) 10, stepping by 3 each time.

Execution Table

Iteration	i (current value)	Condition (i < 10)	Action	Output
1	0	true	print(i), i = i + 3	0
2	3	true	print(i), i = i + 3	3
3	6	true	print(i), i = i + 3	6
4	9	true	print(i), i = i + 3	9
5	12	false	exit loop

💡 i reaches 12, condition 12 < 10 is false, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
i	0	3	6	9	12	12

Key Moments - 3 Insights

Why does the loop stop before printing 12?

Because the condition i < 10 becomes false when i is 12, so the loop exits before printing 12, as shown in execution_table row 5.

What does the 'by' parameter control?

The 'by' parameter controls how much i increases each time, here it adds 3 after each print, as seen in variable_tracker.

Why is the last printed value 9 and not 10?

Because stride uses 'to' which excludes the end value 10, so it stops before reaching 10, shown in the condition checks in execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of i at iteration 3?

A 6

B 9

C 3

D 12

💡 Hint

Check the 'i (current value)' column at iteration 3 in the execution_table.

At which iteration does the condition i < 10 become false?

A 4

B 5

C 3

D 2

💡 Hint

Look at the 'Condition (i < 10)' column in execution_table where it becomes false.

If the 'by' value changed to 4, what would be the output at iteration 2?

A 6

B 3

C 4

D 8

💡 Hint

With 'by' = 4, i increases by 4 each iteration starting from 0, so after first iteration i is 4.

Concept Snapshot

Stride syntax: stride(from: start, to: end, by: step)
Loops from start up to but not including end
Increments by step each time
Stops when current value >= end
Useful for custom step loops

Full Transcript

This visual execution shows how Swift's stride function works with a custom step. Starting at 0, it checks if the current value is less than 10. If yes, it prints the value, then adds 3. This repeats until the value reaches 12, which fails the condition and stops the loop. The variable i changes from 0 to 3, 6, 9, then 12. The loop prints 0, 3, 6, and 9. The step size controls how much i increases each time. The loop excludes the end value 10 because 'to' is used. This helps understand how stride controls loop steps and limits.