Ruby if...else Statement

The Ruby if...else statement is used to execute/skip a block of code based on whether a condition is true or false.

num = 35

# Check if num is a positive number
if num > 0
  puts "Positive number"
# Else, check if num is negative
elsif num < 0
  puts "Negative number"
# If both conditions fail, num is 0
else
  puts "Zero"
end

# Output: Positive number

Ruby if Statement

We use the if keyword to execute code based on some specific condition.

The syntax of the if statement is:

if condition 
  # Block of code
end

The if keyword checks the condition and chooses which code to execute based on the result. If the condition is evaluated to:

• true - The code inside if is executed.
• false - The code inside if is skipped.

Notice the end keyword in the syntax; it is used to indicate the end of the if statement.

Remember: Forgetting to use the end keyword will result in an error.

Example 1: Ruby if Statement

# Program to check if the student passed

score = 96

# Check if score is greater than or equal to 40
if score >= 40
  # The body of the if statement
  puts "You passed the examination."
end

puts "Program executed!"

Output

You passed the examination.
Program executed!

In the above program, the condition score >= 40 evaluates to true since the score is 96. Thus, the body of the if statement is executed.

Had the value of the score been lower than 40 (say, 35), then the body of the if statement wouldn't have been executed.

Finally, since puts "Program executed!" is outside the body of the if statement, it is executed regardless of the results of the if statement.

Tip: Try changing the value of score to something less than 40 and see what happens.

One-line if Statement

Ruby also allows you to use a one-line if statement with the following syntax:

code if condition

Here, code will be executed if the condition is true. For example,

score = 96

puts "You passed!" if score >= 40

# Output: You passed!

Here, the code puts "You passed!" is executed because the condition score >= 40 is true.

Ruby else Statement

The else keyword executes a block of code when the condition in the preceding if statement evaluates to false.

Note: The else statement should always follow an if statement. In other words, the if and else statements are parts of a single conditional structure.

The syntax of the if...else statement is:

if condition
  # Block of code to execute if the condition is true
else
  # Block of code to execute if the condition is false
end

The if...else statement checks condition and executes code in two ways. If condition is:

• true - The code inside if is executed. And, the code inside else is skipped.
• false - The code inside if is skipped. Instead, the code inside else is executed.

Example 2: Ruby if…else Statement

# Program to check if the student passed or failed

score = 35

# Check if score is greater than or equal to 40
if score >= 40
  # The body of the if statement
  puts "You passed the examination."
else
  # The body of the else statement
  puts "You failed the examination."
end

puts "Program executed!"

Output

You failed the examination.
Program executed!

Since score is 35, the if condition (score >= 40) evaluates to false.

Thus, the code inside if is skipped. And, the code inside else is executed.

Ruby elsif Statement

The elsif keyword is used to check for additional conditions if the initial if statement is false.

The syntax of the elsif statement is:

# Check for first condition
if condition1
  # if body

# Check for second condition
elsif condition2
  # elsif body

# If no condition matches
else
  # else body
end

Here:

1. First, the condition in the if statement is checked. If the condition evaluates to true, the body of if is executed, and the rest is skipped.
2. Otherwise, the condition in the elsif statement is checked. If true, its body is executed and the rest is skipped.
3. Finally, if no condition matches, the block of code in else is executed.

Example 3: Ruby if...elsif Statement

score = 59

# Check if score is 80 or above
if score >= 80
  puts "Excellent!"

# Else, check if score is 40 or above
elsif score >= 40
  puts "Average"

# If both conditions fail, you fail the exam
else
  puts "Failure!"
end

# Output: Average

Here, the if condition is false because score is 59. However, the elsif condition is satisfied, so the program prints Average.

score = 85

# Condition for passing with second division
if score >= 40 && score < 60
  puts "Second division"

# Condition for passing with first division
elsif score >= 60 && score < 80
  puts "First division"

# Condition for passing with distinction
elsif score >= 80 && score <= 100
  puts "Distinction"

# Condition for failing the exam
elsif score > 0 && score < 40
  puts "You failed the examination."

# If all conditions fail, the score is invalid
else
  puts "Invalid score!"
end

# Output: Distinction

Nested if...else Statement

When we use an if...else statement inside another if...else statement, we create a nested if...else statement. For example,

score = 60

# Outer if...else statement
# Student passed if score 40 or above
# Otherwise, student failed

if score >= 40

  # Inner if...else statement
  # Distinction if score is 80 or above

  if score >= 80
      puts "Distinction"
  else
      puts "Passed"
  end

else
  puts "Failed"
end

# Output: Passed

Outer if...else Statement

In the above example, the outer if condition checks if a student has passed or failed using the condition score >= 40. If it evaluates to false, the outer else statement will print "Failed".

On the other hand, if score >= 40 evaluates to true, the program moves to the inner if...else statement.

Inner if...else Statement

The inner if condition checks whether the student passed with distinction using the condition score >= 80.

If score >= 80 evaluates to true, the inner if statement will print "Distinction".

Otherwise, the inner else statement will print "Passed".

Note: Avoid nesting multiple if...else statements within each other to maintain code readability and simplify debugging.

score = 40

result = (score >= 40) ? "pass" : "fail"

puts result

# Output: pass

score = "C"

# Using case statement
case score

# First condition
when "A"
  puts "Excellent!"

# Second condition
when "B"
  puts "Good!"

# Third condition
when "C"
  puts "Average"

# Fourth condition
when "D"
  puts "Bad"

else
  puts "Fail"
end

# Output: Average

age = 35
salary = 6000

# Combine two conditions using the "and" operator &&
if age >= 30 && salary >= 5000
  puts "Eligible for premium membership."
else
  puts "Not eligible for premium membership."
end

# Output: Eligible for premium membership.

print "Enter your exam score: "

# Get user input using gets
user_input = gets.chomp

# Convert the input to integer
score = user_input.to_i

# Check if the user passed or failed
if score >= 40
  puts "pass"
else
  puts "fail"
end

Enter your exam score: 56
pass

Enter your exam score: 25
fail