If, elsif, else statements in Ruby - Step-by-Step Execution

Concept Flow - If, elsif, else statements

Start

↓

Check if condition

|Yes↓

Execute if block

↓

End

No↓

Check elsif condition

|Yes↓

Execute elsif block

↓

End

No↓

Execute else block

↓

End

The program checks the if condition first. If true, it runs the if block. If false, it checks the elsif condition. If that is true, it runs the elsif block. Otherwise, it runs the else block.

Execution Sample

Ruby

number = 7
if number < 5
  puts "Less than 5"
elsif number == 7
  puts "Equals 7"
else
  puts "Other number"
end

This code checks a number and prints a message depending on its value.

Execution Table

Step	Condition Checked	Condition Result	Branch Taken	Output
1	number < 5	false	No
2	number == 7	true	Yes	Equals 7
3	else	N/A	No

💡 The elsif condition is true, so the elsif block runs and the rest is skipped.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
number	7	7	7	7

Key Moments - 2 Insights

Why does the else block not run even though it is present?

Because the elsif condition was true at step 2, the program runs that block and skips the else block, as shown in the execution_table row 2.

What happens if the first if condition is true?

If the first if condition is true, the program runs the if block and skips checking the elsif and else blocks, as shown by the flow in concept_flow.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 2?

A Equals 7

B Less than 5

C Other number

D No output

💡 Hint

Check the 'Output' column in execution_table row 2.

At which step does the program decide to skip the else block?

A Step 1

B Step 2

C Step 3

D It never skips the else block

💡 Hint

Look at the 'Branch Taken' column in execution_table rows 2 and 3.

If number was 3, which branch would run according to the execution flow?

A else block

B elsif block

C if block

D No block runs

💡 Hint

Refer to the condition 'number < 5' in execution_table step 1.

Concept Snapshot

if condition
  # code if true
elsif condition
  # code if elsif true
else
  # code if none true
end

Checks conditions in order and runs the first true block only.

Full Transcript

This visual execution shows how Ruby's if, elsif, else statements work. The program starts by checking the if condition. If it is true, it runs that block and skips the rest. If false, it checks the elsif condition. If that is true, it runs the elsif block and skips else. If none are true, it runs the else block. The example code checks if a number is less than 5, equals 7, or something else, and prints a message accordingly. The execution table traces each condition check and the branch taken. The variable tracker shows the number stays the same. Key moments clarify why else is skipped when elsif is true and what happens if the first if is true. The quiz tests understanding of output and flow decisions.

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