Why control flow directs execution in R Programming - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this R code with if-else?

Consider the following R code snippet. What will it print?

R Programming

x <- 5
if (x > 3) {
  print("Greater")
} else {
  print("Smaller")
}

A [1] "Smaller"

B Error: object 'x' not found

C [1] "Greater"

D [1] "Equal"

💡 Hint

Check the condition x > 3 and what it evaluates to.

Since x is 5, which is greater than 3, the if block runs and prints "Greater".

❓ Predict Output

intermediate

What does this for loop print in R?

Look at this R code. What will be the output?

R Programming

for (i in 1:3) {
  if (i == 2) next
  print(i)
}

A [1] 2

B

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

C Error: unexpected symbol in "next print"

D

[1] 1
[1] 3

💡 Hint

The 'next' statement skips the current iteration.

When i is 2, 'next' skips printing 2. So only 1 and 3 are printed.

❓ Predict Output

advanced

What is the output of this nested if-else in R?

Analyze this R code and select the correct output.

R Programming

x <- 0
if (x > 0) {
  print("Positive")
} else if (x == 0) {
  print("Zero")
} else {
  print("Negative")
}

A [1] "Positive"

B [1] "Zero"

C [1] "Negative"

D Error: unexpected 'else' in "} else"

💡 Hint

Check the value of x and which condition matches.

x equals 0, so the else if branch runs and prints "Zero".

❓ Predict Output

advanced

What happens when this R code runs with break inside a while loop?

What will this R code print?

R Programming

i <- 1
while (i <= 5) {
  if (i == 3) break
  print(i)
  i <- i + 1
}

A

[1] 1
[1] 2

B

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

C [1] 3

D Infinite loop

💡 Hint

The break statement stops the loop when i equals 3.

The loop prints 1 and 2, then breaks when i is 3, so 3 is not printed.

❓ Predict Output

expert

What is the value of x after this R code with nested control flow?

Consider this R code. What is the final value of x?

R Programming

x <- 0
for (i in 1:4) {
  if (i %% 2 == 0) {
    x <- x + i
  } else {
    x <- x - i
  }
}

A 2

B -2

C 0

D 4

💡 Hint

Add or subtract i depending on whether it is even or odd.

For i=1 (odd), x=0-1=-1; i=2 (even), x=-1+2=1; i=3 (odd), x=1-3=-2; i=4 (even), x=-2+4=2.

Practice

1. What does control flow in R programming mainly do?

easy

A. Creates new variables without declaration

B. Changes the data types of variables automatically

C. Decides which parts of the code run and when

D. Prints output to the console

Solution

1. Step 1: Understand the role of control flow

   Control flow guides the program to run certain parts of code based on conditions or loops.

2. Step 2: Compare options with control flow purpose

   Only Decides which parts of the code run and when matches this role; others describe unrelated actions.

3. Final Answer:

   Decides which parts of the code run and when -> Option C

4. Quick Check:

   Control flow = directs execution [OK]

Hint: Control flow controls code execution order [OK]

Common Mistakes:

• Confusing control flow with variable creation
• Thinking control flow changes data types
• Assuming control flow prints output

2. Which of the following is the correct syntax for an if statement in R?

easy

A. if x > 5 then print("Yes")

B. if (x > 5) { print("Yes") }

C. if x > 5: print("Yes")

D. if (x > 5) print "Yes"

Solution

1. Step 1: Recall R if statement syntax

   In R, the if statement requires parentheses around the condition and braces for the code block.

2. Step 2: Check each option

   if (x > 5) { print("Yes") } uses correct parentheses and braces. Options B, C, and D use incorrect syntax styles.

3. Final Answer:

   if (x > 5) { print("Yes") } -> Option B

4. Quick Check:

   R if syntax = if(condition) { code } [OK]

Hint: Use parentheses and braces for if in R [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using 'then' keyword (not in R)
• Missing braces for code block

3. What will be the output of this R code?

for (i in 1:3) {
  if (i == 2) {
    print("Skip")
    next
  }
  print(i)
}

medium

A. [1] 1
[1] "Skip"
[1] 3

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

C. [1] 1
[1] 3

D. [1] "Skip"
[1] 3

Solution

1. Step 1: Trace the for loop iterations

   The loop runs i = 1, 2, 3. For i=1, it prints 1. For i=2, it prints "Skip" and uses next to skip printing i. For i=3, it prints 3.

2. Step 2: Understand the effect of next

   next skips the rest of the loop body for i=2, so print(i) is not called then.

3. Final Answer:

   [1] 1 [1] "Skip" [1] 3 -> Option A

4. Quick Check:

   next skips print(i) at i=2 [OK]

Hint: next skips current loop iteration [OK]

Common Mistakes:

• Expecting number 2 to print
• Ignoring next statement effect
• Confusing print order

4. Identify the error in this R code snippet:

i <- 1
while (i < 4) {
  print(i)
  i = i + 1
}

medium

A. The while loop condition is incorrect

B. The increment uses '=' instead of '<-'

C. Missing braces around the while loop body

D. No error, code runs correctly

Solution

1. Step 1: Check while loop syntax

   The while loop uses parentheses for condition and braces for the body, which is correct.

2. Step 2: Check variable increment

   In R, '=' can be used for assignment inside code blocks, so 'i = i + 1' works fine.

3. Final Answer:

   No error, code runs correctly -> Option D

4. Quick Check:

   Both '=' and '<-' assign values in R [OK]

Hint: Both '=' and '<-' assign in R [OK]

Common Mistakes:

• Thinking '=' is invalid for assignment
• Expecting syntax error without braces
• Confusing loop condition syntax

5. You want to print numbers from 1 to 5 but skip 3 using control flow in R. Which code correctly does this?

hard

A. for (i in 1:5) { if (i == 3) next; print(i) }

B. for (i in 1:5) { if (i == 3) break; print(i) }

C. for (i in 1:5) { print(i); if (i == 3) next }

D. for (i in 1:5) { if (i == 3) print(i); else next }

Solution

1. Step 1: Understand the goal

   We want to print numbers 1, 2, 4, 5 but skip printing 3.

2. Step 2: Analyze each option

   for (i in 1:5) { if (i == 3) next; print(i) } uses 'next' to skip printing when i is 3, printing all others. for (i in 1:5) { if (i == 3) break; print(i) } stops loop at 3 (break), so 4 and 5 won't print. for (i in 1:5) { print(i); if (i == 3) next } prints i first then next skips the rest of the body (which is empty), so prints all including 3. for (i in 1:5) { if (i == 3) print(i); else next } prints only 3 and skips others, which is wrong.

3. Step 3: Choose the best control flow usage

   Only for (i in 1:5) { if (i == 3) next; print(i) } correctly uses next to skip exactly 3 and continue the loop.

4. Final Answer:

   for (i in 1:5) { if (i == 3) next; print(i) } -> Option A

5. Quick Check:

   next skips iteration cleanly [OK]

Hint: Use next to skip unwanted loop iterations [OK]

Common Mistakes:

• Using break stops loop early
• Printing only the skipped number
• Not using next to skip iteration
• Placing print before the next check