Ruby program to find factorial of a given number

=begin 
Ruby program to find the factorial of a given number.
=end

puts "Enter the number:"
num=gets.chomp.to_i

fact=1
if (num==0)
    puts "Error! Could not find the factorial of one"
else
    i=1
    while(i<=num)
        fact=fact*i
        i+=1
    end
end
        puts "factorial of #{num} is #{fact}"

Output:

Run 1:
Enter the number:
5
factorial of 5 is 120

Run 2:
Enter the number:
7
factorial of 7 is 5040