While loop in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple while loop

What is the output of the following R code?

R Programming

x <- 1
while (x <= 3) {
  print(x)
  x <- x + 1
}

A

[1] 1
[1] 2

B

[1] 1
[1] 2
[1] 3

C

[1] 1
[1] 2
[1] 3
[1] 4

D Error: object 'x' not found

💡 Hint

The loop runs while x is less than or equal to 3, printing x each time and increasing it by 1.

The loop starts with x = 1 and prints it. Then x increases by 1. This repeats until x becomes 4, which breaks the loop. So it prints 1, 2, and 3.

❓ Predict Output

intermediate

While loop with break statement

What will be printed by this R code?

R Programming

i <- 1
while (TRUE) {
  if (i > 4) break
  print(i)
  i <- i + 1
}

A

[1] 1
[1] 2
[1] 3
[1] 4

B

[1] 1
[1] 2
[1] 3
[1] 4
[1] 5

C Error: object 'i' not found

D

[1] 1
[1] 2
[1] 3

💡 Hint

The loop runs forever until the break condition is met when i is greater than 4.

The loop prints i starting at 1 and increases it by 1 each time. When i becomes 5, the break stops the loop. So it prints 1 to 4.

❓ Predict Output

advanced

While loop with nested if and continue logic

What is the output of this R code?

R Programming

x <- 0
while (x < 5) {
  x <- x + 1
  if (x == 3) next
  print(x)
}

A

[1] 1
[1] 2
[1] 4
[1] 5

B

[1] 1
[1] 2
[1] 3
[1] 4
[1] 5

C

[1] 1
[1] 2
[1] 3
[1] 4

D Error: unexpected symbol in "if (x == 3) next"

💡 Hint

The 'next' statement skips the rest of the loop body when x equals 3.

When x is 3, the 'next' skips the print statement, so 3 is not printed. All other values from 1 to 5 except 3 are printed.

🔧 Debug

advanced

Identify the error in the while loop

What error does this R code produce?

R Programming

count <- 1
while (count < 5) {
  print(count)
  count <- count + 1
}

A Infinite loop printing 1 forever

B Error: object 'count' not found

C Error: unexpected symbol in 'count <- count + 1'

D Prints 1, 2, 3, 4 then stops

💡 Hint

Check the indentation and braces for the while loop body.

With braces, both print and increment are inside the loop, so count increases each iteration until it reaches 5, then loop stops.

🧠 Conceptual

expert

Number of iterations in a while loop

How many times will the loop run in this R code?

R Programming

n <- 10
sum <- 0
while (n > 0) {
  sum <- sum + n
  n <- n - 2
}
sum

A 6

B 10

C 5

D Error: object 'sum' not found

💡 Hint

The loop decreases n by 2 each time until n is no longer greater than 0.

Starting at 10, n decreases by 2 each iteration: 10, 8, 6, 4, 2. After 5 iterations, n becomes 0 and loop stops.

Practice

1. What does a while loop do in R?

easy

A. Executes code only once

B. Repeats code a fixed number of times

C. Repeats code as long as a condition is TRUE

D. Stops the program immediately

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs repeatedly while its condition remains TRUE.

2. Step 2: Compare options

   Only Repeats code as long as a condition is TRUE correctly describes this behavior; others describe different concepts.

3. Final Answer:

   Repeats code as long as a condition is TRUE -> Option C

4. Quick Check:

   while loop = repeat while TRUE [OK]

Hint: While loops run while condition is TRUE, not fixed times [OK]

Common Mistakes:

• Confusing while loop with for loop
• Thinking it runs only once
• Believing it stops the program

2. Which of the following is the correct syntax for a while loop in R?

easy

A. while (i <= 5) { print(i); i <- i + 1 }

B. while i <= 5 { print(i); i <- i + 1 }

C. while i <= 5: print(i); i <- i + 1

D. while (i <= 5) print(i) i <- i + 1

Solution

1. Step 1: Check R while loop syntax

   R requires parentheses around the condition and braces for the loop body.

2. Step 2: Validate each option

   Only while (i <= 5) { print(i); i <- i + 1 } uses correct parentheses and braces syntax.

3. Final Answer:

   while (i <= 5) { print(i); i <- i + 1 } -> Option A

4. Quick Check:

   Correct syntax uses parentheses and braces [OK]

Hint: Use parentheses for condition and braces for loop body [OK]

Common Mistakes:

• Omitting parentheses around condition
• Missing braces for multiple statements
• Using colon or wrong punctuation

3. What is the output of this R code?

i <- 1
while (i <= 3) {
  print(i)
  i <- i + 1
}

medium

A. Error: object 'i' not found

B. [1] 1 [1] 2

C. [1] 3

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

Solution

1. Step 1: Trace the loop iterations

   i starts at 1, loop runs while i <= 3, printing i each time and increasing i by 1.

2. Step 2: List printed values

   Values printed are 1, then 2, then 3 before loop stops.

3. Final Answer:

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

4. Quick Check:

   Prints 1, 2, 3 in order [OK]

Hint: Increment loop variable inside while to avoid infinite loop [OK]

Common Mistakes:

• Forgetting to increment i causing infinite loop
• Expecting only last value printed
• Confusing output format

4. Identify the error in this R while loop code:

i <- 1
while (i < 5) {
  print(i)
}

medium

A. Missing increment of i inside the loop

B. Incorrect condition syntax

C. print() function is invalid

D. Variable i is not initialized

Solution

1. Step 1: Analyze loop body

   The loop prints i but never changes i, so i stays 1 forever.

2. Step 2: Understand consequence

   Without increment, the condition i < 5 is always TRUE, causing infinite loop.

3. Final Answer:

   Missing increment of i inside the loop -> Option A

4. Quick Check:

   Update loop variable to stop loop [OK]

Hint: Always update loop variable inside while to avoid infinite loop [OK]

Common Mistakes:

• Forgetting to increment loop variable
• Assuming print causes increment
• Misreading condition syntax

5. How can you use a while loop in R to calculate the factorial of 5?
Choose the correct code snippet.

hard

A. n <- 5
fact <- 0
i <- 1
while (i < n) {
fact <- fact * i
i <- i + 1
}
fact

B. n <- 5
fact <- 1
i <- 1
while (i <= n) {
fact <- fact * i
i <- i + 1
}
fact

C. n <- 5
fact <- 1
while (n > 0) {
fact <- fact + n
n <- n - 1
}
fact

D. n <- 5
fact <- 1
while (fact <= n) {
fact <- fact * n
n <- n - 1
}
fact

Solution

1. Step 1: Understand factorial calculation

   Factorial multiplies numbers from 1 to n, so loop must multiply fact by i from 1 to n.

2. Step 2: Check each code snippet

   n <- 5 fact <- 1 i <- 1 while (i <= n) { fact <- fact * i i <- i + 1 } fact correctly initializes fact=1, loops i from 1 to n, multiplying fact by i each time.

3. Final Answer:

   n <- 5 fact <- 1 i <- 1 while (i <= n) { fact <- fact * i i <- i + 1 } fact -> Option B

4. Quick Check:

   Multiply 1 to 5 sequentially for factorial [OK]

Hint: Multiply from 1 to n inside while loop for factorial [OK]

Common Mistakes:

• Using addition instead of multiplication
• Incorrect loop condition
• Starting fact at 0 causing zero result