This ruby program finds the input number is prime or not.

prime_number.rb

# this function finds if a number is prime or not
def is_prime_number(number=0)
  # value to store if a number is prime or not 
  # initailly assumed prime
  is_prime=true
  
  #iterate from 2 till half of that number
  for num in 2..(number+1)/2
    
    # check if number is exactly divisible
    # if yes then number will not be prime
    # exit loop
    if number%num==0 
      is_prime=false
      break
    end
  end
  #return value
  return is_prime
end

begin
  
  puts "Enter any number:"
  #take input
  number = Integer(gets.chomp)

#check for prime
if(is_prime_number(number))
  puts "#{number} is prime number"
else
  puts "#{number} is not a prime number"
end
  
#Check if user input was not a Integer  
rescue 
  puts "Enter proper Number."
end