Unless for negated conditions in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print a message unless the number is zero.

Ruby

number = 5
puts "Number is not zero" [1] number == 0

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

Auntil

Bunless

Cwhile

Dif

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'if' instead of 'unless' will print the message only when number is zero.

Using 'while' or 'until' is for loops, not conditions.

In Ruby, unless is used to run code only if the condition is false. Here, it prints the message unless number == 0.

2fill in blank

medium

Complete the code to skip printing when the word is empty using unless.

Ruby

word = "hello"
puts word [1] word.empty?

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

Aif

Bwhile

Cuntil

Dunless

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'if' will print only when the word is empty, which is the opposite of what we want.

Using 'while' or 'until' is for loops, not conditions.

The unless keyword runs the code only if the condition is false. Here, it prints word unless it is empty.

3fill in blank

hard

Fix the error in the code by choosing the correct keyword to print unless the number is negative.

Ruby

number = 3
puts "Positive or zero" [1] number < 0

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

Aunless

Bif

Cwhile

Duntil

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'if' will print only when the number is negative, which is wrong here.

Using 'while' or 'until' is for loops, not conditions.

Using unless here means the message prints only if the number is NOT less than zero (i.e., zero or positive).

4fill in blank

hard

Fill both blanks to create a hash with words as keys and their lengths as values, but only for words longer than 3 letters using unless.

Ruby

words = ["cat", "elephant", "dog", "lion"]
lengths = {}
words.each { |word| lengths[word] = word.length [1] word.length [2] 3 }

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

Aunless

B>

C<=

Dif

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'if' instead of 'unless' changes the logic.

Using '>' instead of '<=' in the condition will include wrong words.

The code uses unless with the condition word.length <= 3 to include only words longer than 3 letters.

5fill in blank

hard

Fill all three blanks to create a hash with uppercase words as keys and their lengths as values, but only for words not empty using unless.

Ruby

words = ["", "apple", "", "banana"]
result = {}
words.each { |word| result[word.[1]] = word.[2] [3] word.empty? }

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

Aupcase

Blength

Cunless

Dif

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'if' instead of 'unless' changes the logic.

Forgetting to convert words to uppercase.

The code uses unless to skip empty words, and stores uppercase words as keys with their lengths as values.

Practice

1. What does the Ruby unless keyword do?

easy

A. Runs the code block regardless of the condition

B. Runs the code block only if the condition is true

C. Runs the code block only if the condition is false

D. Runs the code block twice if the condition is false

Solution

1. Step 1: Understand the purpose of unless

   The unless keyword runs code only when the condition is false, opposite of if.

2. Step 2: Compare with other options

   Options B and C describe if or unconditional execution, D is incorrect behavior.

3. Final Answer:

   Runs the code block only if the condition is false -> Option C

4. Quick Check:

   unless = run if false [OK]

Hint: Think: unless means "if NOT" the condition [OK]

Common Mistakes:

• Confusing unless with if
• Thinking unless runs when condition is true
• Assuming unless runs code twice

2. Which of the following is the correct syntax for using unless in Ruby?

easy

A. unless condition then
puts 'Hello'
end

B. unless condition : puts 'Hello'

C. unless (condition) {
puts 'Hello'
}

D. unless condition
puts 'Hello'
end

Solution

1. Step 1: Recall Ruby block syntax

   Ruby uses unless condition ... end without parentheses or braces for blocks.

2. Step 2: Check each option

   unless condition puts 'Hello' end matches correct Ruby syntax. A uses invalid 'then' with unless, B uses colon incorrectly, C uses braces like other languages.

3. Final Answer:

   unless condition puts 'Hello' end -> Option D

4. Quick Check:

   Ruby blocks use unless condition ... end [OK]

Hint: Use newline and end, not do or braces with unless [OK]

Common Mistakes:

• Adding 'do' after unless
• Using braces {} for unless block
• Using colon instead of newline and end

3. What is the output of this Ruby code?

count = 3
unless count > 5
  puts 'Count is small'
else
  puts 'Count is large'
end

medium

A. Count is small

B. Count is large

C. No output

D. SyntaxError

Solution

1. Step 1: Evaluate the condition count > 5

   Given count = 3, the condition 3 > 5 is false.

2. Step 2: Apply unless logic

   unless runs the first block if condition is false, so it prints 'Count is small'.

3. Final Answer:

   Count is small -> Option A

4. Quick Check:

   Condition false -> unless runs first block [OK]

Hint: Remember unless runs when condition is false [OK]

Common Mistakes:

• Thinking unless runs when condition is true
• Confusing else block execution
• Expecting no output

4. Find the error in this Ruby code using unless:

unless x = 10
  puts 'x is not 10'
end

medium

A. unless cannot be used with variables

B. Assignment (=) used instead of comparison (==) in condition

C. Missing end keyword

D. puts statement should be outside unless block

Solution

1. Step 1: Identify the condition mistake

   The code uses x = 10 which assigns 10 to x, always true, instead of comparing with ==.

2. Step 2: Understand impact on unless

   Since assignment returns 10 (truthy), unless condition is true, so block won't run. This is likely a bug.

3. Final Answer:

   Assignment (=) used instead of comparison (==) in condition -> Option B

4. Quick Check:

   Use == for comparison, not = [OK]

Hint: Use == to compare, = is assignment [OK]

Common Mistakes:

• Using = instead of == in conditions
• Thinking unless needs else always
• Assuming no error with assignment in condition

5. You want to print "Access denied" only when a user is NOT an admin. Which Ruby code using unless is correct?

hard

A. unless user.admin?
puts 'Access denied'
end

B. unless user.admin?
puts 'Access granted'
end

C. if !user.admin?
puts 'Access denied'
end

D. if user.admin?
puts 'Access denied'
end

Solution

1. Step 1: Understand the condition needed

   We want to print 'Access denied' only if user is NOT admin.

2. Step 2: Match condition with unless

   unless user.admin? runs block if user.admin? is false, exactly when user is not admin.

3. Step 3: Check other options

   unless user.admin? puts 'Access granted' end prints wrong message, C uses if with negation (correct but not using unless), D prints denied when user is admin (wrong).

4. Final Answer:

   unless user.admin? puts 'Access denied' end -> Option A

5. Quick Check:

   Use unless for negated condition [OK]

Hint: Use unless for simple negated conditions [OK]

Common Mistakes:

• Mixing messages with wrong conditions
• Using if with negation instead of unless
• Printing denied when user is admin