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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a for loop.

R Programming

for (i in [1]) {
  print(i)
}

Drag options to blanks, or click blank then click option'

Aseq(5, 1)

Bc(1, 5)

C1:5

Drange(1, 5)

Attempts:

3 left

💡 Hint

Common Mistakes

Using range(1, 5) which is not valid in R.

Using seq(5, 1) which counts backwards.

The expression 1:5 creates a sequence from 1 to 5 in R, which the for loop uses to print numbers 1 through 5.

2fill in blank

medium

Complete the code to check if a number x is positive and print a message.

R Programming

if ([1] > 0) {
  print("Positive")
}

Drag options to blanks, or click blank then click option'

Ax

Bx != 0

Cx < 0

Dx == 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using x == 0 which checks for zero, not positive.

Using x < 0 which checks for negative numbers.

The condition x > 0 checks if x is positive. Here, x is the variable being compared.

3fill in blank

hard

Fix the error in the code to print 'Even' for even numbers.

R Programming

if (x [1] 2 == 0) {
  print("Even")
}

Drag options to blanks, or click blank then click option'

Arem

Bmod

Cdiv

D%%

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'mod' or 'rem' which are not valid operators in R.

Using 'div' which is not an operator in R.

The modulo operator in R is %%, which gives the remainder of division. Using x %% 2 == 0 checks if x is even.

4fill in blank

hard

Fill both blanks to create a vector of squares of numbers greater than 3.

R Programming

squares <- c()
for ([2] in 1:5) {
  if ([2] > 3) {
    squares <- c(squares, [1]^2)
  }
}

Drag options to blanks, or click blank then click option'

Ax

Bi

Cfor

Dy

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the two blanks.

Using 'for' which is a keyword, not a variable.

In R, to create a vector of squares for numbers greater than 3, you use a loop variable like i. Both blanks need the same variable name i.

5fill in blank

hard

Fill all three blanks to create a named list of numbers greater than 2 with their squares.

R Programming

result <- list()
for ([3] in 1:5) {
  if ([3] > 2) {
    result[[paste0([1], [3] )]] <- [2]^2
  }
}

Drag options to blanks, or click blank then click option'

Anum

Bi

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for the loop variable.

Using invalid names for the list element.

The list is named with num, the loop variable is i, and the expression uses i to compute squares for numbers greater than 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