Until loop in Ruby - Step-by-Step Execution

Concept Flow - Until loop

Initialize variable

↓

Check condition

↓

EXIT

↓

Update variable

↩Back to Check

The until loop runs the code inside it until the condition becomes true. It checks the condition first, and if false, runs the loop body.

Execution Sample

Ruby

i = 0
until i > 3
  puts i
  i += 1
end

Prints numbers from 0 to 3 using an until loop that stops when i becomes greater than 3.

Execution Table

Step	i	Condition (i > 3)	Condition Result	Action	Output
1	0	0 > 3	False	Print i=0, i = i + 1	0
2	1	1 > 3	False	Print i=1, i = i + 1	1
3	2	2 > 3	False	Print i=2, i = i + 1	2
4	3	3 > 3	False	Print i=3, i = i + 1	3
5	4	4 > 3	True	Exit loop

💡 At step 5, condition i > 3 is True, so the loop stops.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
i	0	1	2	3	4	4

Key Moments - 2 Insights

Why does the loop stop when i is 4, not when i is 3?

Because the condition is 'i > 3'. When i is 3, 3 > 3 is false, so the loop runs. When i becomes 4, 4 > 3 is true, so the loop stops (see execution_table step 5).

Does the loop run if the condition is true at the start?

No, the until loop checks the condition before running. If the condition is true initially, the loop body does not run at all.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i at step 3?

A 1

B 2

C 3

D 4

💡 Hint

Check the 'i' column in execution_table row for step 3.

At which step does the condition become true and the loop stops?

A Step 5

B Step 4

C Step 3

D Step 2

💡 Hint

Look at the 'Condition Result' column in execution_table to find when it becomes True.

If the initial value of i was 5, what would happen?

A The loop runs once

B The loop runs infinitely

C The loop does not run at all

D The loop runs twice

💡 Hint

Recall that until loop runs only if condition is false initially (see key_moments about initial condition).

Concept Snapshot

Ruby until loop syntax:
until condition
  # code runs while condition is false
end

It checks condition first.
Runs loop body only if condition is false.
Stops when condition becomes true.

Full Transcript

This visual execution shows how the Ruby until loop works. We start with i = 0. The loop checks if i > 3. Since 0 > 3 is false, it runs the loop body: prints i and adds 1 to i. This repeats until i becomes 4, where 4 > 3 is true, so the loop stops. The variable i changes from 0 to 4 step by step. The key point is that the until loop runs while the condition is false and stops when it becomes true. If the condition is true at the start, the loop does not run at all.