For loop (rarely used in Ruby) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 3 using a for loop.

Ruby

for i in [1]
  puts i
end

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

Arange(1,3)

B[1, 2, 3, 4]

C1...3

D1..3

Attempts:

3 left

💡 Hint

Common Mistakes

Using Python-style range function which doesn't exist in Ruby.

Using exclusive range 1...3 which excludes 3.

The for loop iterates over the range 1..3, which includes 1, 2, and 3.

2fill in blank

medium

Complete the code to print each fruit in the array using a for loop.

Ruby

fruits = ["apple", "banana", "cherry"]
for [1] in fruits
  puts fruit
end

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

Afruit

Bitem

Cf

Dfruits

Attempts:

3 left

💡 Hint

Common Mistakes

Using the array name fruits as the loop variable.

Using a variable name that is not used inside the loop.

The variable fruit is used to represent each element in the fruits array during the loop.

3fill in blank

hard

Fix the error in the for loop to correctly print numbers from 1 to 5.

Ruby

for i in [1]
  puts i
end

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

A1...5

B1..5

Crange(1, 5)

D[1, 2, 3, 4]

Attempts:

3 left

💡 Hint

Common Mistakes

Using exclusive range 1...5 which excludes 5.

Using Python-style range which is invalid in Ruby.

The range 1..5 includes the number 5, so the loop prints 1 through 5.

4fill in blank

hard

Fill both blanks to create a for loop that prints only even numbers from 2 to 10.

Ruby

for num in [1]
  puts num if num [2] 0
end

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

A2..10

B% 2 ==

C% 2 !=

D1..10

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong range that starts at 1.

Using % 2 != 0 which checks for odd numbers.

The loop iterates from 2 to 10. The condition num % 2 == 0 checks if the number is even before printing.

5fill in blank

hard

Fill all three blanks to create a for loop that prints squares of numbers from 1 to 5 only if the square is greater than 10.

Ruby

for [1] in [2]
  square = [1] * [1]
  puts square if square > 10
end

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

An

B1..5

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Using a range that does not include 5.

The loop variable n goes from 1 to 5. The square is calculated by multiplying n by itself. Only squares greater than 10 are printed.

Practice

1. What does the following Ruby for loop do?

for i in 1..3
puts i
end

easy

A. Prints numbers 1, 2, and 3 each on a new line

B. Prints numbers 1 to 2 only

C. Prints numbers 0 to 3

D. Causes a syntax error

Solution

1. Step 1: Understand the range 1..3

   The range 1..3 includes the numbers 1, 2, and 3.

2. Step 2: Loop through each number and print

   The loop prints each number on its own line using puts.

3. Final Answer:

   Prints numbers 1, 2, and 3 each on a new line -> Option A

4. Quick Check:

   for loop with 1..3 prints 1, 2, 3 [OK]

Hint: Remember 1..3 includes 3, so loop prints 1, 2, 3 [OK]

Common Mistakes:

• Thinking 1..3 excludes 3
• Confusing puts with print
• Expecting syntax error

2. Which of the following is the correct syntax for a for loop in Ruby to iterate over an array ["a", "b", "c"]?

easy

A. for x to ["a", "b", "c"] puts x end

B. for (x : ["a", "b", "c"]) puts x end

C. for x in ["a", "b", "c"] do puts x end

D. for x in ["a", "b", "c"] puts x

Solution

1. Step 1: Check the correct Ruby for loop syntax

   Ruby uses for variable in collection do ... end or without do.

2. Step 2: Validate each option

   for x in ["a", "b", "c"] do puts x end uses correct syntax with for x in array do ... end. for (x : ["a", "b", "c"]) puts x end and C use invalid syntax. for x in ["a", "b", "c"] puts x misses end to close the loop.

3. Final Answer:

   for x in ["a", "b", "c"] do puts x end -> Option C

4. Quick Check:

   Correct Ruby for loop uses 'for x in collection do ... end' [OK]

Hint: Remember: for x in collection do ... end is correct Ruby syntax [OK]

Common Mistakes:

• Using colon or 'to' instead of 'in'
• Omitting the 'end' keyword
• Adding parentheses incorrectly

3. What is the output of this Ruby code?

sum = 0
for i in 1..4
sum += i
end
puts sum

medium

A. Error

B. 9

C. 0

D. 10

Solution

1. Step 1: Understand the loop range and sum initialization

   The loop runs from 1 to 4, and sum starts at 0.

2. Step 2: Calculate sum after each iteration

   sum = 0+1=1, then 1+2=3, then 3+3=6, then 6+4=10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Sum of 1 to 4 is 10 [OK]

Hint: Add numbers 1 through 4 to get 10 quickly [OK]

Common Mistakes:

• Forgetting to include last number 4
• Starting sum at 1 instead of 0
• Syntax errors in loop

4. Identify the error in this Ruby for loop:

for i in 1..3
puts i


medium

A. Wrong range syntax

B. Missing end to close the loop

C. Variable i not defined

D. Using puts inside loop is invalid

Solution

1. Step 1: Check loop syntax completeness

   The loop starts with for but does not have a matching end.

2. Step 2: Confirm other parts are correct

   The range 1..3 and variable i are valid, and puts is allowed inside loops.

3. Final Answer:

   Missing end to close the loop -> Option B

4. Quick Check:

   Every for loop needs an 'end' [OK]

Hint: Always close for loops with 'end' [OK]

Common Mistakes:

• Forgetting 'end' keyword
• Thinking variable must be declared first
• Believing puts is invalid inside loops

5. You want to create a Ruby for loop that prints only even numbers from 2 to 10 inclusive. Which code snippet achieves this correctly?

hard

A. for i in 2..10 do
puts i if i % 2 == 0
end

B. for i in 2..10 do
puts i if i % 2 == 1
end

C. for i in 1..10 do
puts i if i % 2 == 1
end

D. for i in 2..10
puts i
end

Solution

1. Step 1: Identify the range and condition for even numbers

   The range 2..10 includes numbers 2 through 10. Even numbers satisfy i % 2 == 0.

2. Step 2: Check each option's condition

   for i in 2..10 do puts i if i % 2 == 0 end prints numbers in 2..10 only if even. for i in 2..10 do puts i if i % 2 == 1 end prints odd numbers. for i in 1..10 do puts i if i % 2 == 1 end prints odd numbers 1,3,5,7,9. for i in 2..10 puts i end prints all numbers without filtering.

3. Final Answer:

   for i in 2..10 do puts i if i % 2 == 0 end -> Option A

4. Quick Check:

   Filter with 'if i % 2 == 0' inside for loop [OK]

Hint: Use 'if i % 2 == 0' inside for loop to print evens [OK]

Common Mistakes:

• Using wrong modulo condition for even numbers
• Not filtering numbers inside loop
• Starting range at 1 instead of 2