Solution: Compute Pi

print "Enter the number of terms for the approximation: "
n = gets.chomp.to_i * 2
pi = 0
plus = true
(1..n).step(2) do |x|  # each step is equal to 1 + 2x
  if plus  
     pi += 1.0 / x
  else
     pi -= 1.0 / x 
  end
  plus = !plus
end

pi = pi * 4
puts "My computation PI = #{pi}"
puts "   Ruby's PI value: #{Math::PI}"