Repeat loop with break in R Programming - Step-by-Step Execution

Concept Flow - Repeat loop with break

Start repeat loop

↓

Execute loop body

↓

Check break condition

↓

Exit loop

The repeat loop runs its body repeatedly until a break condition is met, then it exits.

Execution Sample

R Programming

i <- 1
repeat {
  print(i)
  if (i == 3) break
  i <- i + 1
}

This code prints numbers from 1 to 3 using a repeat loop and breaks when i equals 3.

Execution Table

Step	i value	Condition (i == 3)?	Action	Output
1	1	No	Print 1; i <- 2	1
2	2	No	Print 2; i <- 3	2
3	3	Yes	Print 3; break loop	3
4	-	-	Loop exits	-

💡 At step 3, condition i == 3 is True, so break exits the loop.

Variable Tracker

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

Key Moments - 2 Insights

Why does the loop stop after printing 3?

Because at step 3 in the execution_table, the condition i == 3 is True, triggering the break statement which exits the loop immediately.

What happens if the break condition is never met?

The repeat loop would run forever because repeat loops only stop when break is called, as shown by the loop continuing when condition is No in steps 1 and 2.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of i at step 2?

A 2

B 1

C 3

D 4

💡 Hint

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

At which step does the loop exit?

A Step 2

B Step 4

C Step 3

D Step 1

💡 Hint

Look at the 'Action' column where break is called in the execution_table.

If we change the break condition to i == 5, what will happen to the output?

A It will print 1 to 3 and stop

B It will print 1 to 5 and then stop

C It will print 1 to 4 and then stop

D It will run forever without stopping

💡 Hint

i increments by 1 each loop after print if condition false; it will print 1-5 then break when i==5.

Concept Snapshot

repeat {
  # code
  if (condition) break
}

- repeat runs forever until break
- break exits loop immediately
- useful for loops with complex exit conditions

Full Transcript

This example shows how a repeat loop in R runs repeatedly until a break condition is met. We start with i = 1. Each loop prints i, then checks if i equals 3. If yes, break stops the loop. Otherwise, i increases by 1 and the loop repeats. The execution table tracks each step, showing i values, condition checks, actions, and output. The variable tracker shows how i changes after each iteration. Key moments clarify why the loop stops at 3 and what happens if break is never reached. The quiz tests understanding of i values, loop exit step, and effects of changing the break condition.

Practice

1.

What does the repeat loop do in R?

Choose the best description.

easy

A. It runs code only once and then stops automatically.

B. It runs code repeatedly until a break statement stops it.

C. It runs code a fixed number of times without stopping early.

D. It runs code only if a condition is true at the start.

Solution

1. Step 1: Understand the repeat loop behavior and compare options

   The repeat loop in R runs indefinitely until a break is encountered. Only "It runs code repeatedly until a break statement stops it." correctly describes that the loop runs repeatedly until break stops it.

2. Final Answer:

   It runs code repeatedly until a break statement stops it. -> Option B

3. Quick Check:

   repeat loop = runs until break [OK]

Hint: Remember: repeat loops run forever until break stops them [OK]

Common Mistakes:

• Thinking repeat loops run a fixed number of times
• Confusing repeat with for or while loops
• Assuming repeat loops stop automatically without break

2.

Which of the following is the correct syntax to start a repeat loop in R?

?

easy

A. repeat { }

B. repeat() { }

C. repeat[] { }

D. repeat do { }

Solution

1. Step 1: Recall the syntax of repeat loops in R and check options

   The correct syntax is repeat { ... } without parentheses or other symbols. Only repeat { } matches the correct syntax exactly.

2. Final Answer:

   repeat { } -> Option A

3. Quick Check:

   repeat loop syntax = repeat { } [OK]

Hint: repeat loops use braces {} without parentheses [OK]

Common Mistakes:

• Adding parentheses after repeat
• Using square brackets instead of braces
• Using keywords like do with repeat

3.

What will be the output of this R code?

i <- 1
repeat {
  if (i > 3) break
  print(i)
  i <- i + 1
}

medium

A. No output, infinite loop

B. [1] 1
[1] 2
[1] 3
[1] 4

C. [1] 1
[1] 2

D. [1] 1
[1] 2
[1] 3

Solution

1. Step 1: Trace the loop iterations

   i starts at 1. Loop checks if i > 3, breaks if true. Otherwise, prints i and increments i by 1. When i becomes 4, condition i > 3 is true, so break stops the loop. Values printed are 1, 2, and 3 before break.

2. Final Answer:

   [1] 1 [1] 2 [1] 3 -> Option D

3. Quick Check:

   Prints 1 to 3 then breaks [OK]

Hint: Loop breaks when i > 3, so prints 1,2,3 only [OK]

Common Mistakes:

• Expecting it to print 4
• Thinking it runs infinitely
• Forgetting to increment i

4.

Find the error in this R code using repeat and break:

count <- 1
repeat {
  print(count)
  if (count == 5)
    break
}

medium

A. The variable count is never incremented, causing an infinite loop.

B. The break statement is outside the loop.

C. The repeat loop syntax is incorrect.

D. The if condition should be count > 5.

Solution

1. Step 1: Check loop variable changes and behavior

   The variable count is printed but never increased, so it stays 1 forever. Since count never reaches 5, break is never triggered, causing an infinite loop.

2. Final Answer:

   The variable count is never incremented, causing an infinite loop. -> Option A

3. Quick Check:

   Missing increment causes infinite loop [OK]

Hint: Always update loop variables to avoid infinite loops [OK]

Common Mistakes:

• Forgetting to increment the loop counter
• Misplacing the break statement
• Incorrect loop syntax assumptions

5.

Write a repeat loop in R that prints numbers from 10 down to 1 and then stops.

Which code snippet correctly does this?

?

hard

A. i <- 10
repeat {
print(i)
i <- i - 1
if (i < 0) break
}

B. i <- 10
repeat {
print(i)
i <- i + 1
if (i == 0) break
}

C. i <- 10
repeat {
print(i)
if (i == 1) break
i <- i - 1
}

D. i <- 1
repeat {
print(i)
i <- i + 1
if (i > 10) break
}

Solution

1. Step 1: Understand the counting direction and check options

   We want to print from 10 down to 1, then stop. So i starts at 10 and decreases by 1 each loop. i <- 10 repeat { print(i) i <- i - 1 if (i < 0) break } prints i, then decrements i, and breaks when i < 0, so it prints 10 down to 0 inclusive, but since break is after decrement, it stops after printing 0. To print 10 down to 1, break should be when i < 1. i <- 10 repeat { print(i) if (i == 1) break i <- i - 1 } prints i, breaks when i == 1, then decrements i, so it prints 10 down to 1 correctly and stops. Therefore, i <- 10 repeat { print(i) if (i == 1) break i <- i - 1 } is the correct code snippet.

2. Final Answer:

   i <- 10 repeat { print(i) if (i == 1) break i <- i - 1 } -> Option C

3. Quick Check:

   Counts down 10 to 1 then breaks [OK]

Hint: Break after printing 1 to include it in output [OK]

Common Mistakes:

• Breaking before printing 1, missing last number
• Incrementing instead of decrementing
• Wrong break condition causing infinite loop