Question

How to compute the factorial of a number greater than 20 in Ruby

Answer 1

#
#   This program computes the factorial of numbers greater than 20.
#   Ruby's Integer type automatically expands to arbitrary size,
#   making it ideal for very large factorials.
#

#
#   Compute factorial using Ruby's built‑in big‑integer support.
#   The algorithm multiplies numbers from 2 to n.
#
def factorial_big(n)
  result = 1

  (2..n).each do |i|
    result *= i
  end

  result
end

#
#   Main entry point: read input, compute factorial, print result.
#
print "Enter a number greater than 20: "
n = Integer(gets.chomp)

result = factorial_big(n)

puts "\nFactorial of #{n} is:\n\n"
puts result


#
# run:
#
# Enter a number greater than 20: 25
# 
# Factorial of 25 is:
# 
# 15511210043330985984000000
#

 

70+ SQL courses for beginners and professionals