decrementing arrays

**santosh** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

Bill Cunningham wrote:

I don't know if I'll need pointers for this or not. I wants numbers
10^16. Like a credit card 16 digits of possible 10 numbers,

Your question is not clear. Do you want an integer type that can store
values upto 1e16? Do you want an array of 16 integers each of which can
hold a ten digit decimal value?

so I guess that would be 10^16. So I have
>
int num [16][10];
These are of course declared and not initialized. Now I want to
initialize them all with '\0'.

Why? Why not just zero?

That I'm guessing would involve while (
--). Or maybe for. Would pointers be involved in this?

Why should they be explicitly involved.

With this excercise I would learn working with multi-dimensional
arrary, maybe pointers and initializing to zero. I tried to do this
using putchar so I obviously don't know what to do. Can someone help
me learn this?

So you want to set that array to zero? Do:

for (int i = 0; i < 16; i++)
for (int j = 0; j < 10; j++)
num[i][j] = 0;

**Bill Cunningham** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"santosh" <santosh.k83@gm ail.comwrote in message
news:g3h26k$444 $1@registered.m otzarella.org.. .

So you want to set that array to zero? Do:
>
for (int i = 0; i < 16; i++)
for (int j = 0; j < 10; j++)
num[i][j] = 0;

Wow thanks Santosh. I've seen things like this in code but the i's j's k's
and so on start to blur after awhile and I just give up. So now I know what
that means. What about randomizing ? So all is set to zero. Would srand be
involved ?

Bill

-----
"You big Dummy" --Fred Sanford

>

**Bill Cunningham** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"santosh" <santosh.k83@gm ail.comwrote in message
news:g3h26k$444 $1@registered.m otzarella.org.. .

So you want to set that array to zero? Do:
>
for (int i = 0; i < 16; i++)
for (int j = 0; j < 10; j++)
num[i][j] = 0;

Why is there a =0 after num [i][j] ?

Bill

-----
"You big dummy" --Fred Sanford

**Ben Bacarisse** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Bill Cunningham" <nospam@nspam.c omwrites:

I don't know if I'll need pointers for this or not. I wants numbers
10^16. Like a credit card 16 digits of possible 10 numbers, so I guess that
would be 10^16. So I have
>
int num [16][10];

That is an array of 16 arrays of 10 ints. To store ten things, each
of which is 16 elements long you would write:

T num[10][16];

where T is the element type. int is not the obvious choice here.
char is quite big enough to store a single digit. You will have
trouble if you think these arrays will behave like strings. To so
that you'd need 17 elements in each to allow for a null at the end of
even the longest ones.

These are of course declared and not initialized. Now I want to initialize
them all with '\0'.

That is an odd thing to initial an integer array with, but it works.
It is the same as 0.

That I'm guessing would involve while ( --). Or maybe
for. Would pointers be involved in this?

Not for initialising:

int num[16][10] = {'\0'};

and it is done.

With this excercise I would learn working with multi-dimensional
arrary, maybe pointers and initializing to zero. I tried to do this using
putchar so I obviously don't know what to do. Can someone help me learn
this?

Are you sure you know enough about 1-dimensional arrays? I will be
hard to learn about arrays of arrays if the base concept is at all
hazy.

--
Ben.

**Bill Cunningham** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Ben Bacarisse" <ben.usenet@bsb .me.ukwrote in message
news:87od5vvoqx .fsf@bsb.me.uk. ..

"Bill Cunningham" <nospam@nspam.c omwrites:

Would pointers be involved in this?

>
Not for initialising:
>
int num[16][10] = {'\0'};
>
and it is done.

Are you sure Ben? I am not the one to be questioning you but I was told
or atleast my understanding from the past has been to to this.

Ok char
char num[10]={0,0,0,0,0,0,0 ,0,0,0};

but char num[10]={'\0'}; Is certainly easier.

Bill
-----
"You big dummy" --Fred Sanford

**Bill Cunningham** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

What if I wanted to look at the value of one element in the array. One
dimensional and multi dimensional?

printf("%c\n",n um[5]); ?

Bill
-----
"You big dummy" --Fred Sanford

**Richard** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Bill Cunningham" <nospam@nspam.c omwrites:

I don't know if I'll need pointers for this or not. I wants numbers
10^16. Like a credit card 16 digits of possible 10 numbers, so I guess that
would be 10^16. So I have
>
int num [16][10];
These are of course declared and not initialized. Now I want to initialize
them all with '\0'. That I'm guessing would involve while ( --). Or maybe
for. Would pointers be involved in this?
>
With this excercise I would learn working with multi-dimensional
arrary, maybe pointers and initializing to zero. I tried to do this using
putchar so I obviously don't know what to do. Can someone help me learn
this?
>
Bill
>
-----
"You Big Dummy" -- Fred Sanford

You surprise me more and more.

Firstly what you want is a single credit card number. Which is 16 digits
of 0-9.

I doubt very very much you are doing any calculations with this number.

So simply store it as a string : zero terminated or not.

char CCNum[] ="0123456789012 345"; /* zero terminated credit card number as a
string */

If you want to learn pointers simply go out and buy some and wave them
around.

**santosh** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

Bill Cunningham wrote:

>
"santosh" <santosh.k83@gm ail.comwrote in message
news:g3h26k$444 $1@registered.m otzarella.org.. .
>

>So you want to set that array to zero? Do:
>>
> for (int i = 0; i < 16; i++)
> for (int j = 0; j < 10; j++)
> num[i][j] = 0;

>
Why is there a =0 after num [i][j] ?

Because it's the same as using '\0' and more logical. Use '\0' for char
arrays and 0 for arrays of short, int, long, long long etc., and use
NULL to initialise arrays of pointers.

**Bill Cunningham** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Richard" <rgrdev@gmail.c omwrote in message
news:g3h4l2$fem $1@registered.m otzarella.org.. .

You surprise me more and more.

Is that good or bad :-)

Firstly what you want is a single credit card number. Which is 16 digits
of 0-9.
>
I doubt very very much you are doing any calculations with this number.
>
So simply store it as a string : zero terminated or not.

What do you mean zero terminated or not? Doesn't C stick \0
automatically ? The only exception I know is strlen.

Bill

-----
"You big dummy" --Fred Sanford

**Ben Bacarisse** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Bill Cunningham" <nospam@nspam.c omwrites:

"Ben Bacarisse" <ben.usenet@bsb .me.ukwrote in message
news:87od5vvoqx .fsf@bsb.me.uk. ..

>"Bill Cunningham" <nospam@nspam.c omwrites:

Would pointers be involved in this?
>

>>
>Not for initialising:
>>
>int num[16][10] = {'\0'};
>>
>and it is done.

>
Are you sure Ben?

Yes.

And, by the way, to set to 0 later you don't need a loop:

memset(num, 0, sizeof num);

will do it if num is an array of integer types (chars, ints, etc) but
check back here if num is a parameter -- that complicates things.

--
Ben.

**Ben Bacarisse** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Bill Cunningham" <nospam@nspam.c omwrites:

What if I wanted to look at the value of one element in the array. One
dimensional and multi dimensional?
>
printf("%c\n",n um[5]); ?

No. num[5] is an array-valued expression -- it will be converted to a
pointer to the first element. %c can't be used with an int * argument
(num was declared int num[16][10]).

I can't suggest what you should use, because I don't know what you
want to do.

--
Ben.

**Richard** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Bill Cunningham" <nospam@nspam.c omwrites:

"Richard" <rgrdev@gmail.c omwrote in message
news:g3h4l2$fem $1@registered.m otzarella.org.. .
>
>

>You surprise me more and more.

>
Is that good or bad :-)
>

>Firstly what you want is a single credit card number. Which is 16 digits
>of 0-9.
>>
>I doubt very very much you are doing any calculations with this number.
>>
>So simply store it as a string : zero terminated or not.

>
What do you mean zero terminated or not? Doesn't C stick \0
automatically ? The only exception I know is strlen.
>
Bill
>
-----
"You big dummy" --Fred Sanford

I mean you might not need it to be zero terminated since you know its
length is always 16. But better to be I dare say in your code and makes
it easier for display.

But I guess you understood what I sad?

Solving a problem is all about analysing the problem. And you are making
problems there for yourself that are not there.

All that 10^16 stuff was nonsense.

**Bill Cunningham** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Ben Bacarisse" <ben.usenet@bsb .me.ukwrote in message
news:877icjvmd3 .fsf@bsb.me.uk. ..

I can't suggest what you should use, because I don't know what you
want to do.

I used %c because it was suggested I use an array of type char. If char
num [10][17] contained different numbers how could I view a specific
element's value of the array using printf? I think that might answer all my
questions if I could know this.

Thanks

Bill
--
"You big dummy" --Fred Sanford

https://www.youtube.com/watch?v=tOuFA0jNaac

**Keith Thompson** · Jun 27 '08, 07:42 PM

Re: decrementing arrays

"Bill Cunningham" <nospam@nspam.c omwrites:

"Richard" <rgrdev@gmail.c omwrote in message
news:g3h4l2$fem $1@registered.m otzarella.org.. .

[...]

>So simply store it as a string : zero terminated or not.

>
What do you mean zero terminated or not? Doesn't C stick \0
automatically ? The only exception I know is strlen.

You're right, and Richard is wrong. A string is zero-terminated *by
definition*.

I think what Richard meant is to use an array of char. The array can
be zero-terminated (making it a string), or not zero-terminated (in
which case it's not a string).

I'm not convinced a character array is the best approach; I'll post a
separate followup.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

decrementing arrays

decrementing arrays

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