I created a class for prime numbers as so:
class Primes
def initialize
end
def prime?(number)
# Method returns true if number is prime.
limit = Math.sqrt(number).ceil
flag = true
if number % 2 == 0
flag = false
else
3.step(limit,2) {|i|
if number % i == 0
flag = false
break
end
}
end
return flag
end
def show_primes(lower, upper)
# Prints all primes between lower and upper
# Lower is incremented 1 if it is even.
# The arcane "(((lower/2).floor)*2+1)" performs this task
(((lower/2).floor)*2+1).step(upper,2) {|i|
if prime?(i) == true
print i.to_s + " "
end
}
end
Then when I enter
a=primes.new
a.show_primes(1000000,1000100) I get
1000003 1000033 1000037 1000039 1000081 1000099 1000001
Where is that trailing 1000001 coming from? It is not a prime number and
in fact is the lower limit.
If I enter the same methods outside of class Primes and enter
show_primes(1000000,1000100) I don't get the lower limit at the end of
the printed values.
I am running version 1.18.4 using scite in Ubuntu.
--
Charles Gray -- Phoenix, AZ; Where you can bake the chill out of your
bones
The value of the #step method is the initial value so that is being returned from a.show_primes and presumably printed by whatever you're using to interpret your statements (like irb):
With your code in a file names "primes.rb"
$ irb -rprimes
>> a=Primes.new
=> #<Primes:0x6e5d88>
>> a.show_primes(1_000_000, 1_000_100)
1000003 1000033 1000037 1000039 1000081 1000099 => 1000001
>> a.show_primes(1_000_000, 1_000_100); nil
1000003 1000033 1000037 1000039 1000081 1000099 => nil
>> a.show_primes(1_000_000, 1_000_100); puts ""
1000003 1000033 1000037 1000039 1000081 1000099
=> nil
Note that the value of the last expression is displayed by irb itself. (In the last example, the puts supplies a newline and the value of puts as an expression is nil.)
To see the documentation for the step method (after first trying Fixnum#step and Integer#step rather than looking it up in the pickaxe 
$ ri -T Numeric#step
----------------------------------------------------------- Numeric#step
num.step(limit, step ) {|i| block } => num
···
On Dec 26, 2006, at 8:20 PM, Charles A Gray wrote:
------------------------------------------------------------------------
Invokes _block_ with the sequence of numbers starting at _num_,
incremented by _step_ on each call. The loop finishes when the
value to be passed to the block is greater than _limit_ (if _step_
is positive) or less than _limit_ (if _step_ is negative). If all
the arguments are integers, the loop operates using an integer
counter. If any of the arguments are floating point numbers, all
are converted to floats, and the loop is executed _floor(n +
n*epsilon)+ 1_ times, where _n = (limit - num)/step_. Otherwise,
the loop starts at _num_, uses either the +<+ or +>+ operator to
compare the counter against _limit_, and increments itself using
the +++ operator.
1.step(10, 2) { |i| print i, " " }
Math::E.step(Math::PI, 0.2) { |f| print f, " " }
_produces:_
1 3 5 7 9
2.71828182845905 2.91828182845905 3.11828182845905
-Rob
Rob Biedenharn http://agileconsultingllc.com
Rob@AgileConsultingLLC.com
