Ruby Program to Check Even or Odd Number

In Ruby, you can check if a number is even or odd using number.even? or number.odd? methods. For example, puts 4.even? ? 'Even' : 'Odd' prints 'Even'.

Examples

Input4

OutputEven

Input7

OutputOdd

Input0

OutputEven

How to Think About It

To check if a number is even or odd, think about dividing it by 2. If the number divides evenly with no remainder, it is even; otherwise, it is odd. Ruby provides simple methods to check this directly.

Algorithm

1

Get the input number.

2

Check if the number is divisible by 2 without remainder.

3

If yes, print 'Even'.

4

Otherwise, print 'Odd'.

Code

ruby

puts 'Enter a number:'
number = gets.to_i
if number.even?
  puts 'Even'
else
  puts 'Odd'
end

Output

Enter a number:
4
Even

Dry Run

Let's trace the input 4 through the code

1

Input number

User enters 4, stored in variable number = 4

2

Check even?

4.even? returns true because 4 % 2 == 0

3

Print result

Since true, prints 'Even'

Step	number	number.even?	Output
1	4	true	Even

Why This Works

Step 1: Getting input

We ask the user to enter a number and convert it to an integer with gets.to_i.

Step 2: Checking evenness

The even? method returns true if the number divides by 2 with no remainder.

Step 3: Printing result

If even? is true, we print 'Even'; otherwise, we print 'Odd'.

Alternative Approaches

Using modulo operator

ruby

puts 'Enter a number:'
number = gets.to_i
if number % 2 == 0
  puts 'Even'
else
  puts 'Odd'
end

This uses the modulo operator to check remainder; it is more manual but works the same.

Using ternary operator

ruby

puts 'Enter a number:'
number = gets.to_i
puts number.even? ? 'Even' : 'Odd'

This is a shorter way using a one-line conditional expression.

Complexity: O(1) time, O(1) space

Time Complexity

Checking if a number is even or odd is a simple arithmetic operation that takes constant time.

Space Complexity

The program uses a fixed amount of memory regardless of input size.

Which Approach is Fastest?

Using even? or modulo operator both run in constant time; even? is more readable.

Approach	Time	Space	Best For
Using even? method	O(1)	O(1)	Readability and simplicity
Using modulo operator	O(1)	O(1)	Manual control and understanding basics
Using ternary operator	O(1)	O(1)	Concise code for simple checks