Repeat loop with break in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a repeat loop in R?

A repeat loop in R runs the code inside it indefinitely until a break statement stops it.

beginner

How do you stop a repeat loop in R?

You stop a repeat loop by using the break statement inside the loop when a condition is met.

beginner

What happens if you forget to use break in a repeat loop?

The loop will run forever, causing your program to freeze or crash because it never stops.

beginner

Example: What does this code do?

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

This code prints numbers 1, 2, and 3. It stops the loop when i equals 3 using break.

intermediate

Why use a repeat loop instead of a for or while loop?

Use repeat when you want to keep looping until a condition inside the loop tells it to stop, without specifying the number of iterations upfront.

What keyword stops a repeat loop in R?

A end

B stop

C break

D exit

The break keyword immediately stops the loop.

What happens if a repeat loop has no break?

A It throws an error

B It runs forever

C It runs once

D It skips the loop

Without break, the repeat loop never stops and runs forever.

Which of these is a correct way to stop a repeat loop when i equals 5?

A if (i == 5) break

B if (i = 5) stop

C if (i == 5) exit

D if (i == 5) end

The correct syntax to stop the loop is if (i == 5) break.

What will this code print?

i <- 1
repeat {
  print(i)
  if (i >= 2) break
  i <- i + 1
}

A 1, 2, and 3

B Only 1

C Only 2

D 1 and 2

It prints 1 first, then 2, then stops because i >= 2 becomes true.

Why might you choose a repeat loop over a while loop?

A When you want to check the stop condition inside the loop body

B When you know the number of iterations in advance

C When you want to run the loop exactly once

D When you want to avoid using <code>break</code>

A repeat loop runs indefinitely until a break inside the loop stops it, so you check the stop condition inside the loop body.

Explain how a repeat loop works in R and how you stop it.

Think about what happens if you never use break.

Write a simple example of a repeat loop that prints numbers 1 to 4 and then stops.

Use a variable to count and break when it reaches 4.

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