Forum: Ruby A newbie question about scanf

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Ken K. (Guest)
on 2006-06-01 03:34
I tried to get user input by using scanf

a = scanf('%d')

that works, it's all very nice, until i do this

while a < 100
and a is an array, so i can't do that.

So i did this
while a[0] < 100...

which works... but is there a better way of doing it?

thanks in advance!
Hal F. (Guest)
on 2006-06-01 04:18
(Received via mailing list)
Ken K. wrote:
> while a[0] < 100...
>
> which works... but is there a better way of doing it?

These should all work:

   a, = scanf('%d')
   a,* = scanf('%d')    # Prettier
   a = *scanf('%d')     # Clearer?

However, if you really just want to convert a single
string to an integer, use str.to_i or Integer(str).


Hal
Ken K. (Guest)
on 2006-06-01 04:29
Hal F. wrote:
> Ken K. wrote:
>> while a[0] < 100...
>>
>> which works... but is there a better way of doing it?
>
> These should all work:
>
>    a, = scanf('%d')
>    a,* = scanf('%d')    # Prettier
>    a = *scanf('%d')     # Clearer?
>
> However, if you really just want to convert a single
> string to an integer, use str.to_i or Integer(str).
>
>
> Hal

Hmmm... the * thing...
is it possible if you explain that in a bit more detail? Is that like
pointers in C?
Hal F. (Guest)
on 2006-06-01 04:51
(Received via mailing list)
Ken K. wrote:
> is it possible if you explain that in a bit more detail? Is that like
> pointers in C?

No... it's what David Alan Black calls the "unary unarray" operator,
also called the "splat" operator.

* on an array turns it into a simple list (sort of like removing
the brackets).

Actually... I think I misled you on the third example.
I don't think it works. You'd still need more than one
item on the left side if you used it.

On the other side, it's different.

    x,* = array   # means the same as
    x,  = array   # but with the * it looks better

x gets assigned the first value.

There's also:

   a = scanf('%d')[0]    # or
   a = scanf('%d').first



Hal
Jeff P. (Guest)
on 2006-06-01 06:17
As a fellow newbie, let me just say that this splat business is all very
interesting, but I get cornfused one step earlier.  You all seem to
think it is quite ordinary that this scanf method returns an array.
What's up with that?  If it gathers one line of input, why then, 'o why
doesn't it return a string object????

thanks,
jp




Hal F. wrote:
> Ken K. wrote:
>> is it possible if you explain that in a bit more detail? Is that like
>> pointers in C?
>
> No... it's what David Alan Black calls the "unary unarray" operator,
> also called the "splat" operator.
>
> * on an array turns it into a simple list (sort of like removing
> the brackets).
>
> Actually... I think I misled you on the third example.
> I don't think it works. You'd still need more than one
> item on the left side if you used it.
>
> On the other side, it's different.
>
>     x,* = array   # means the same as
>     x,  = array   # but with the * it looks better
>
> x gets assigned the first value.
>
> There's also:
>
>    a = scanf('%d')[0]    # or
>    a = scanf('%d').first
>
>
>
> Hal
Hal F. (Guest)
on 2006-06-01 07:00
(Received via mailing list)
Jeff P. wrote:
> As a fellow newbie, let me just say that this splat business is all very
> interesting, but I get cornfused one step earlier.  You all seem to
> think it is quite ordinary that this scanf method returns an array.
> What's up with that?  If it gathers one line of input, why then, 'o why
> doesn't it return a string object????

scanf typically returns multiple objects -- it reads a string and
returns strings, integers, floats, whatever.

The case where you're only reading one item is the oddball
case. I guess it would be possible to just "return the item" --
but it's more natural to return an array always.

Hal
Jeff P. (Guest)
on 2006-06-01 07:35
OH!  Now I remember.  Haven't used it in forever.  It uses a format
string just like printf.  The returned array would be it's best attempt
to pick out all of the pieces that the format string asked for.  Makes
sense now.

thanks,
jp


Hal F. wrote:
> Jeff P. wrote:
>> As a fellow newbie, let me just say that this splat business is all very
>> interesting, but I get cornfused one step earlier.  You all seem to
>> think it is quite ordinary that this scanf method returns an array.
>> What's up with that?  If it gathers one line of input, why then, 'o why
>> doesn't it return a string object????
>
> scanf typically returns multiple objects -- it reads a string and
> returns strings, integers, floats, whatever.
>
> The case where you're only reading one item is the oddball
> case. I guess it would be possible to just "return the item" --
> but it's more natural to return an array always.
>
> Hal
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