If, elsif, else statements in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of an if statement in Ruby?

An if statement lets the program choose to run some code only when a condition is true.

beginner

How do you write an elsif in Ruby?

Use elsif to check another condition if the first if condition is false. It comes after if and before else.

beginner

What does the else part do in an if statement?

else runs code when all previous if and elsif conditions are false.

intermediate

Write a simple Ruby if-elsif-else statement that prints 'Cold', 'Warm', or 'Hot' based on a temperature variable.

Example:

temp = 30
if temp < 10
  puts 'Cold'
elsif temp < 25
  puts 'Warm'
else
  puts 'Hot'
end

intermediate

Can you have multiple elsif branches in one if statement?

Yes, you can have many elsif branches to check several conditions in order.

What will this Ruby code print?

if false
  puts 'Yes'
else
  puts 'No'
end

A No

B Error

C Nothing

D Yes

Since the condition is false, the else block runs and prints 'No'.

Which keyword checks a second condition if the first if is false?

A else

B elsif

C when

D case

elsif lets you check another condition after if.

What happens if none of the if or elsif conditions are true and there is no else?

A The program crashes

B The last condition runs anyway

C No code inside runs

D It runs the first block

If no conditions match and no else exists, no code inside the statement runs.

How do you end an if statement in Ruby?

A end

B endif

C done

D finish

Ruby uses end to close if statements.

Which is the correct order in Ruby conditional statements?

A else, if, elsif

B elsif, if, else

C if, else, elsif

D if, elsif, else

The order is if, then zero or more elsif, then optional else.

Explain how if, elsif, and else work together in Ruby.

Think of it like choosing one path out of many based on conditions.

Write a Ruby example using if, elsif, and else to decide what to wear based on temperature.

Use temperature ranges to decide clothes.

Practice

1.

What does the elsif keyword do in Ruby?

easy

A. It ends the if statement.

B. It runs code only if all previous conditions were true.

C. It checks another condition if the previous if or elsif was false.

D. It repeats the if block multiple times.

Solution

1. Step 1: Understand the role of elsif

   The elsif keyword is used to check another condition only if the previous if or elsif condition was false.

2. Step 2: Compare with other options

   Options A, C, and D describe behaviors that do not match elsif. It does not end the statement, nor repeats code, nor runs only if all previous conditions were true.

3. Final Answer:

   It checks another condition if the previous if or elsif was false. -> Option C

4. Quick Check:

   elsif = check next condition [OK]

Hint: Remember: elsif checks next condition if previous false [OK]

Common Mistakes:

• Thinking elsif ends the if statement
• Confusing elsif with else
• Assuming elsif runs only if all previous are true

2.

Which of the following is the correct syntax for an if statement with an else in Ruby?

?

easy

A. if x > 10
puts "Big"
else
puts "Small"
end

B. if (x > 10) {
puts "Big"
} else {
puts "Small"
}

C. if x > 10 then puts "Big" else puts "Small"

D. if x > 10:
puts "Big"
else:
puts "Small"

Solution

1. Step 1: Identify Ruby syntax for if and else

   Ruby uses if condition, then code indented or on next line, and ends with end. Curly braces or colons are not used.

2. Step 2: Check each option

   if x > 10 puts "Big" else puts "Small" end matches Ruby syntax exactly. Options A, B, and C use syntax from other languages like colons (A), braces (B), or missing end (C).

3. Final Answer:

   if x > 10 puts "Big" else puts "Small" end -> Option A

4. Quick Check:

   Ruby if ends with end [OK]

Hint: Ruby if always ends with end [OK]

Common Mistakes:

• Using braces {} instead of end
• Forgetting the end keyword
• Using colons like Python

3.

What will be the output of this Ruby code?

score = 75
if score >= 90
  puts "Grade A"
elsif score >= 80
  puts "Grade B"
elsif score >= 70
  puts "Grade C"
else
  puts "Grade F"
end

medium

A. Grade A

B. Grade B

C. Grade F

D. Grade C

Solution

1. Step 1: Check conditions in order

   score is 75. First condition: score >= 90 is false. Second: score >= 80 is false. Third: score >= 70 is true.

2. Step 2: Output for first true condition

   Since third condition is true, it prints "Grade C" and skips the rest.

3. Final Answer:

   Grade C -> Option D

4. Quick Check:

   75 >= 70 is true, so output is Grade C [OK]

Hint: Check conditions top to bottom; first true runs [OK]

Common Mistakes:

• Choosing Grade B or A without checking order
• Ignoring that only first true condition runs
• Confusing >= with >

4.

Find the error in this Ruby code snippet:

number = 10
if number > 5
  puts "Big"
elsif number < 3
  puts "Small"
else
  puts "Medium"

medium

A. Wrong keyword elsif should be else if.

B. Missing end to close the if statement.

C. The puts statements need parentheses.

D. The comparison operators are incorrect.

Solution

1. Step 1: Check Ruby syntax completeness

   Ruby if statements must end with end. The code snippet is missing end.

2. Step 2: Verify other parts

   elsif is correct in Ruby. puts can be used without parentheses. Comparison operators are correct.

3. Final Answer:

   Missing end to close the if statement. -> Option B

4. Quick Check:

   Every if needs end [OK]

Hint: Always close if with end [OK]

Common Mistakes:

• Replacing elsif with else if
• Adding unnecessary parentheses to puts
• Changing correct comparison operators

5.

You want to write a Ruby program that prints "Positive", "Negative", or "Zero" depending on the value of num. Which code correctly uses if, elsif, and else to do this?

hard

A. if num > 0
puts "Positive"
elsif num < 0
puts "Negative"
else
puts "Zero"
end

B. if num >= 0
puts "Positive"
elsif num <= 0
puts "Negative"
else
puts "Zero"
end

C. if num > 0
puts "Positive"
else if num < 0
puts "Negative"
else
puts "Zero"
end

D. if num > 0
puts "Positive"
elsif num > 0
puts "Negative"
else
puts "Zero"
end

Solution

1. Step 1: Understand the conditions needed

   We want to print "Positive" if num > 0, "Negative" if num < 0, and "Zero" otherwise.

2. Step 2: Check each option's logic

   if num > 0 puts "Positive" elsif num < 0 puts "Negative" else puts "Zero" end matches the logic exactly with correct if, elsif, and else. if num >= 0 puts "Positive" elsif num <= 0 puts "Negative" else puts "Zero" end wrongly treats zero as positive. if num > 0 puts "Positive" else if num < 0 puts "Negative" else puts "Zero" end uses invalid else if syntax in Ruby. if num > 0 puts "Positive" elsif num > 0 puts "Negative" else puts "Zero" end repeats the same condition twice, which is incorrect.

3. Final Answer:

   if num > 0 puts "Positive" elsif num < 0 puts "Negative" else puts "Zero" end -> Option A

4. Quick Check:

   Correct conditions and syntax = if num > 0 puts "Positive" elsif num < 0 puts "Negative" else puts "Zero" end [OK]

Hint: Use elsif for second condition, else for default [OK]

Common Mistakes:

• Using else if instead of elsif
• Repeating same condition in elsif
• Misclassifying zero as positive or negative