A newbie question about scanf

Ruby
1

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!

2

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

3

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?

4

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

5

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

6

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

7

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