From: "Michael W. Ryder" <_mwryder@...>
Date: 2007-03-21T04:00:11+09:00
Subject: Re: C(++) For Loop Equivalents

Pe�a wrote:
> From: Michael W. Ryder [mailto:_mwryder@worldnet.att.net] :
> 
> # He would need to initialize i before your code as it could be 
> # any value, 
> # not just 0.  By the same token the increment could be any number, not 
> # just 1.
> 
> fwiw, this is a simple example (intended for nubies only). 
> 
> C:\family\ruby>cat -n test.rb
>      1  #---------------------------
>      2  #emulate c++ for (the better)
>      3  #for(int i=0; i*j/2<maxNum; i++)
>      4  # {
>      5  #  //cool method stuff
>      6  # }
>      7  #---------------------------
>      8
>      9  # using normal while loop
>     10  puts "using while..."
>     11  j=20
>     12  i=0
>     13  maxnum=100
>     14  while i*j/2 < maxnum do
>     15     puts i
>     16     i+=1
>     17  end
>     18
>     19  # let's make our own for() and call it for_simple :)
>     20  # note, there's no condition here
>     21  # we're leaving it up to yield/blocks since that
>     22  # is the ideal way, imho
>     23  def for_simple (init=0,incr=1)
>     24     i = init
>     25     loop do
>     26        yield i
>     27        i += incr
>     28     end
>     29  end
>     30
>     31  # now let's test it
>     32  puts <<TEXT
>     33  Test I.
>     34  using our own simple for()...  note advantage,
>     35  we don't need to track the counter...
>     36  TEXT
>     37
>     38  for_simple do |i|
>     39     break unless i*j/2 < maxnum
>     40     puts i
>     41  end
>     42
>     43  puts <<TEXT
>     44  Test II.
>     45  here we initialize to 2 and increment by 2
>     46  again, we don't need to track the counter...
>     47  TEXT
>     48
>     49  for_simple(2,2) do |i|
>     50     break unless i*j/2 < maxnum
>     51     puts i
>     52  end
>     53
>     54  puts <<TEXT
>     55  Test III.
>     56  again, here we initialize to 200 and decrement by 20
>     57  again, we don't need to track the counter...
>     58  and note, we change keyword unless to if
>     59  ruby just simply rocks..
>     60  TEXT
>     61
>     62  for_simple(200,-20) do |i|
>     63     break if i*j/2 < maxnum
>     64     puts i
>     65  end
> 
> C:\family\ruby>ruby test.rb
> using while...
> 0
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> Test I.
> using our own simple for()...  note advantage,
> we don't need to track the counter...
> 0
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> Test II.
> here we initialize to 2 and increment by 2
> again, we don't need to track the counter...
> 2
> 4
> 6
> 8
> Test III.
> again, here we initialize to 200 and decrement by 20
> again, we don't need to track the counter...
> and note, we change keyword unless to if
> ruby just simply rocks..
> 200
> 180
> 160
> 140
> 120
> 100
> 80
> 60
> 40
> 20
> 
> C:\family\ruby>
> 
> Hth.
> kind regards -botp
> 
>

Now is it possible, like in Scheme, to assign a variable to a string and 
have Ruby evaluate the string?  For example, f = "i*j/2".  This would 
allow one to make a more generic version of your methods.  Ideally you 
would have for_opt (i=0, f, inc=1) and have the method evaluate each of 
the variables if necessary.  This would allow one to copy working C code 
without having to remember to do a lot of extraneous coding.