How do I "read-in" numbers from the left?

I have something like this:

printf("Enter numbers: ");
scanf ("%i", &number);

If the user put in a bunch of numbers (like 4568), instead of just one
number, i know that you can extract the right most digit with this:

right_number = number % 10;
/* print the number */
number = number / 10;

Well, i have the above setup in a loop, so i keep getting the right
most digit printed out. However, they're all backwards since i am
reading in the right-most digit first. How do i make it so it reads
the left-most first, and then proceeds to print? Or is there a way to
flip the right most ones around afterwards?

I can only use printf, scanf and switch functions right now.

Thx.

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> I have something like this:
>
> printf("Enter numbers: ");
> scanf ("%i", &number);
>
> If the user put in a bunch of numbers (like 4568), instead of just one
> number, i know that you can extract the right most digit with this:
>
> right_number = number % 10;
> /* print the number */
> number = number / 10;
>
> Well, i have the above setup in a loop, so i keep getting the right most
> digit printed out. However, they're all backwards since i am reading in
> the right-most digit first. How do i make it so it reads the left-most
> first, and then proceeds to print? Or is there a way to flip the right
> most ones around afterwards?
>
> I can only use printf, scanf and switch functions right now.
>
> Thx.
>
>[/color]

if you want to read digits from left to right, c provides recursives functions...

Xavier

re: How do I "read-in" numbers from the left?

on 2/20/2006, serrand supposed :[color=blue]
> gk245 wrote:[color=green]
>> I have something like this:
>>
>> printf("Enter numbers: ");
>> scanf ("%i", &number);
>>
>> If the user put in a bunch of numbers (like 4568), instead of just one
>> number, i know that you can extract the right most digit with this:
>>
>> right_number = number % 10;
>> /* print the number */
>> number = number / 10;
>>
>> Well, i have the above setup in a loop, so i keep getting the right most
>> digit printed out. However, they're all backwards since i am reading in
>> the right-most digit first. How do i make it so it reads the left-most
>> first, and then proceeds to print? Or is there a way to flip the right most
>> ones around afterwards?
>>
>> I can only use printf, scanf and switch functions right now.
>>
>> Thx.
>>
>>[/color]
>
> if you want to read digits from left to right, c provides recursives
> functions...
>
> Xavier[/color]

Well, thats the thing. I am not allowed to use those functions, only
printf, scanf, switch, and if-else statments.

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> on 2/20/2006, serrand supposed :
>[color=green]
>> gk245 wrote:
>>[color=darkred]
>>> I have something like this:
>>>
>>> printf("Enter numbers: ");
>>> scanf ("%i", &number);
>>>
>>> If the user put in a bunch of numbers (like 4568), instead of just
>>> one number, i know that you can extract the right most digit with this:
>>>
>>> right_number = number % 10;
>>> /* print the number */
>>> number = number / 10;
>>>
>>> Well, i have the above setup in a loop, so i keep getting the right
>>> most digit printed out. However, they're all backwards since i am
>>> reading in the right-most digit first. How do i make it so it reads
>>> the left-most first, and then proceeds to print? Or is there a way to
>>> flip the right most ones around afterwards?
>>>
>>> I can only use printf, scanf and switch functions right now.
>>>
>>> Thx.
>>>
>>>[/color]
>>
>> if you want to read digits from left to right, c provides recursives
>> functions...
>>
>> Xavier[/color]
>
>
> Well, thats the thing. I am not allowed to use those functions, only
> printf, scanf, switch, and if-else statments.
>
>[/color]

then you can try something like
....
if ( (int)(n/100000) != 0) printf ("%d", (int)(n/100000));
if ( (int)(n/10000) != 0) ...
....

not very nice... but it works with your req ...
Despite... nothing to do with standard c ...

Xavier

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> on 2/20/2006, serrand supposed :
>[color=green]
>> gk245 wrote:
>>[color=darkred]
>>> I have something like this:
>>>
>>> printf("Enter numbers: ");
>>> scanf ("%i", &number);
>>>
>>> If the user put in a bunch of numbers (like 4568), instead of just
>>> one number, i know that you can extract the right most digit with this:
>>>
>>> right_number = number % 10;
>>> /* print the number */
>>> number = number / 10;
>>>
>>> Well, i have the above setup in a loop, so i keep getting the right
>>> most digit printed out. However, they're all backwards since i am
>>> reading in the right-most digit first. How do i make it so it reads
>>> the left-most first, and then proceeds to print? Or is there a way to
>>> flip the right most ones around afterwards?
>>>
>>> I can only use printf, scanf and switch functions right now.
>>>
>>> Thx.
>>>
>>>[/color]
>>
>> if you want to read digits from left to right, c provides recursives
>> functions...
>>
>> Xavier[/color]
>
>
> Well, thats the thing. I am not allowed to use those functions, only
> printf, scanf, switch, and if-else statments.
>
>[/color]

it seeems to bee an algorithmic problem...
Find the left most digit then proceed...
if ((int)(n/100...0) != 0)
{
/**/ then extract one by one digit with substractions ...
}
else


better :

k = scanf ("%c%c%c%c%c%c%c%c%c", &n);
k == number of digits... then go on

Xavier

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> I have something like this:
>
> printf("Enter numbers: ");
> scanf ("%i", &number);
>
> If the user put in a bunch of numbers (like 4568), instead of just one
> number, i know that you can extract the right most digit with this:
>
> right_number = number % 10;
> /* print the number */
> number = number / 10;
>
> Well, i have the above setup in a loop, so i keep getting the right
> most digit printed out. However, they're all backwards since i am
> reading in the right-most digit first. How do i make it so it reads
> the left-most first, and then proceeds to print? Or is there a way to
> flip the right most ones around afterwards?
>
> I can only use printf, scanf and switch functions right now.
>
> Thx.[/color]

It seems you could input the number as a string using scanf() even
though using scanf has a bug (but you cannot use fgets). Once you have
the input, start accessing the left most number using index 0, 1, and
so on..

So, the code snippet could be:

scanf("%s", str);
str[0] = .... /* To acess the first digit */

Now if you want that character as a numeral digit you could do
str[index]-'0' (Assuming ASCII).

Hope that helps.

re: How do I "read-in" numbers from the left?

Jaspreet expressed precisely :[color=blue]
> gk245 wrote:[color=green]
>> I have something like this:
>>
>> printf("Enter numbers: ");
>> scanf ("%i", &number);
>>
>> If the user put in a bunch of numbers (like 4568), instead of just one
>> number, i know that you can extract the right most digit with this:
>>
>> right_number = number % 10;
>> /* print the number */
>> number = number / 10;
>>
>> Well, i have the above setup in a loop, so i keep getting the right
>> most digit printed out. However, they're all backwards since i am
>> reading in the right-most digit first. How do i make it so it reads
>> the left-most first, and then proceeds to print? Or is there a way to
>> flip the right most ones around afterwards?
>>
>> I can only use printf, scanf and switch functions right now.
>>
>> Thx.[/color]
>
> It seems you could input the number as a string using scanf() even
> though using scanf has a bug (but you cannot use fgets). Once you have
> the input, start accessing the left most number using index 0, 1, and
> so on..
>
> So, the code snippet could be:
>
> scanf("%s", str);
> str[0] = .... /* To acess the first digit */
>
> Now if you want that character as a numeral digit you could do
> str[index]-'0' (Assuming ASCII).
>
> Hope that helps.[/color]

Hmm, %s i might be able to use somehow. However, i can't use arrays.
:-(.

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> Jaspreet expressed precisely :[color=green]
> > gk245 wrote:[color=darkred]
> >> I have something like this:
> >>
> >> printf("Enter numbers: ");
> >> scanf ("%i", &number);
> >>
> >> If the user put in a bunch of numbers (like 4568), instead of just one
> >> number, i know that you can extract the right most digit with this:
> >>
> >> right_number = number % 10;
> >> /* print the number */
> >> number = number / 10;
> >>
> >> Well, i have the above setup in a loop, so i keep getting the right
> >> most digit printed out. However, they're all backwards since i am
> >> reading in the right-most digit first. How do i make it so it reads
> >> the left-most first, and then proceeds to print? Or is there a way to
> >> flip the right most ones around afterwards?
> >>
> >> I can only use printf, scanf and switch functions right now.
> >>
> >> Thx.[/color]
> >
> > It seems you could input the number as a string using scanf() even
> > though using scanf has a bug (but you cannot use fgets). Once you have
> > the input, start accessing the left most number using index 0, 1, and
> > so on..
> >
> > So, the code snippet could be:
> >
> > scanf("%s", str);
> > str[0] = .... /* To acess the first digit */
> >
> > Now if you want that character as a numeral digit you could do
> > str[index]-'0' (Assuming ASCII).
> >
> > Hope that helps.[/color]
>
> Hmm, %s i might be able to use somehow. However, i can't use arrays.
> :-(.[/color]

You surely have lots of restrictions in place. If you cannot use
arrays, then I guess Xavier did give a solution in a previous post. You
could input the number character by character and then try and use them
to solve your problem.

re: How do I "read-in" numbers from the left?

"Jaspreet" <jsingh.oberoi@gmail.com> wrote in message
news:1140480229.168954.251910@g47g2000cwa.googlegr oups.com...[color=blue]
> Now if you want that character as a numeral digit you could do
> str[index]-'0' (Assuming ASCII).[/color]

As people pointed out to me in some other thread, this does not apply just
to ASCII. It is generally true because the Standard ensures it.

re: How do I "read-in" numbers from the left?

"gk245" <topsoil@mail.com> wrote in message
news:mn.a4067d627f0b04be.49793@mail.com...[color=blue]
> I have something like this:
>
> printf("Enter numbers: ");
> scanf ("%i", &number);
>
> If the user put in a bunch of numbers (like 4568), instead of just one
> number, i know that you can extract the right most digit with this:
>
> right_number = number % 10;
> /* print the number */
> number = number / 10;
>
> Well, i have the above setup in a loop, so i keep getting the right
> most digit printed out. However, they're all backwards since i am
> reading in the right-most digit first. How do i make it so it reads
> the left-most first, and then proceeds to print? Or is there a way to
> flip the right most ones around afterwards?
>
> I can only use printf, scanf and switch functions right now.
>
> Thx.[/color]

I do not know if you are "allowed" this but anyway take a look, printdec()
is recursive:

#include <stdio.h>

void printdec(unsigned int i)
{
if (i/10) printdec(i/10);
printf("%d",i%10);
fflush(stdout);
}

int main(void)
{
unsigned int number;

printf("Enter numbers: ");
scanf ("%d", &number);

printdec(number);
printf("\n");

return 0;
}

It can print non-negative numbers in their decimal representation.
I tried to keep your own code too, even if it is not that safe. You can work
out the rest.

re: How do I "read-in" numbers from the left?

Jaspreet wrote:
[color=blue]
> It seems you could input the number as a string using scanf() even
> though using scanf has a bug (but you cannot use fgets). Once you have
> the input, start accessing the left most number using index 0, 1, and
> so on..
>
> So, the code snippet could be:
>
> scanf("%s", str);
> str[0] = .... /* To acess the first digit */
>
> Now if you want that character as a numeral digit you could do
> str[index]-'0' (Assuming ASCII).[/color]

ASCII is irrelevant to the validity of the
(str[index]-'0') expression.

--
pete

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> I have something like this:
>
> printf("Enter numbers: ");
> scanf ("%i", &number);
>
> If the user put in a bunch of numbers (like 4568), instead of just one
> number, i know that you can extract the right most digit with this:
>
> right_number = number % 10;
> /* print the number */
> number = number / 10;
>
> Well, i have the above setup in a loop, so i keep getting the right most
> digit printed out. However, they're all backwards since i am reading in
> the right-most digit first. How do i make it so it reads the left-most
> first, and then proceeds to print? Or is there a way to flip the right
> most ones around afterwards?
>
> I can only use printf, scanf and switch functions right now.
>
> Thx.
>
>[/color]

from left to right or right to left, without arrays, without any extra call but scanf

int n, m, i;
char c;
n = 0;
m = 0;
i = 1;
while (scanf ("%c", &c), c != '\n')
{
n = 10*n + (c-'0');
m += i*(c-'0');
i *= 10;
}
printf ("N = %d %d\n", n, m);

Xavier

re: How do I "read-in" numbers from the left?

serrand formulated the question :[color=blue]
> gk245 wrote:[color=green]
>> I have something like this:
>>
>> printf("Enter numbers: ");
>> scanf ("%i", &number);
>>
>> If the user put in a bunch of numbers (like 4568), instead of just one
>> number, i know that you can extract the right most digit with this:
>>
>> right_number = number % 10;
>> /* print the number */
>> number = number / 10;
>>
>> Well, i have the above setup in a loop, so i keep getting the right most
>> digit printed out. However, they're all backwards since i am reading in
>> the right-most digit first. How do i make it so it reads the left-most
>> first, and then proceeds to print? Or is there a way to flip the right most
>> ones around afterwards?
>>
>> I can only use printf, scanf and switch functions right now.
>>
>> Thx.
>>
>>[/color]
>
> from left to right or right to left, without arrays, without any extra call
> but scanf
>
> int n, m, i;
> char c;
> n = 0;
> m = 0;
> i = 1;
> while (scanf ("%c", &c), c != '\n')
> {
> n = 10*n + (c-'0');
> m += i*(c-'0');
> i *= 10;
> }
> printf ("N = %d %d\n", n, m);
>
> Xavier[/color]

wow, thats impressive. 8-o

re: How do I "read-in" numbers from the left?

pete wrote:[color=blue]
> Jaspreet wrote:
>[color=green]
> > It seems you could input the number as a string using scanf() even
> > though using scanf has a bug (but you cannot use fgets). Once you have
> > the input, start accessing the left most number using index 0, 1, and
> > so on..
> >
> > So, the code snippet could be:
> >
> > scanf("%s", str);
> > str[0] = .... /* To acess the first digit */
> >
> > Now if you want that character as a numeral digit you could do
> > str[index]-'0' (Assuming ASCII).[/color]
>
> ASCII is irrelevant to the validity of the
> (str[index]-'0') expression.
>
> --
> pete[/color]

Yes realised after I had posted. Not sure why I wrote "assuming ASCII".
Apologies for that.

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> I have something like this:
>
> printf("Enter numbers: ");
> scanf ("%i", &number);
>
> If the user put in a bunch of numbers (like 4568), instead of just one
> number, i know that you can extract the right most digit with this:
>
> right_number = number % 10;
> /* print the number */
> number = number / 10;
>
> <snip>
>
> I can only use printf, scanf and switch functions right now.
>[/color]

#include <stdio.h>

int main (void)
{
int num = 0, revnum = 0, digit = 0;

printf ("Enter a number: ");
scanf ("%i", &num);

while (num > 0)
{
digit = num % 10;
revnum = revnum*10 + digit;
num /= 10;
}

printf ("Reversed number is %d\n", revnum);
return 0;
}

re: How do I "read-in" numbers from the left?

Sirius Black has brought this to us :[color=blue]
> gk245 wrote:[color=green]
>> I have something like this:
>>
>> printf("Enter numbers: ");
>> scanf ("%i", &number);
>>
>> If the user put in a bunch of numbers (like 4568), instead of just one
>> number, i know that you can extract the right most digit with this:
>>
>> right_number = number % 10;
>> /* print the number */
>> number = number / 10;
>>
>> <snip>
>>
>> I can only use printf, scanf and switch functions right now.
>>[/color]
>
> #include <stdio.h>
>
> int main (void)
> {
> int num = 0, revnum = 0, digit = 0;
>
> printf ("Enter a number: ");
> scanf ("%i", &num);
>
> while (num > 0)
> {
> digit = num % 10;
> revnum = revnum*10 + digit;
> num /= 10;
> }
>
> printf ("Reversed number is %d\n", revnum);
> return 0;
> }[/color]

I might be reading this the wrong way, but if revnum is set to zero
from the beginning, then revnum*10 will always equal zero. So the
expression 'revnum = revnum*10 + digit' is just goint to set revnum to
the digit's value..... i don't see why revnum*10 is needed since all
its saying is that 0*10 + digit.

Apologies if i am wrong...

thanks.

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> Sirius Black has brought this to us :[color=green]
>> #include <stdio.h>[/color]
> I might be reading this the wrong way, but if revnum is set to zero from
> the beginning, then revnum*10 will always equal zero.[/color]

No, if you check the code right, you'll see that "revnum*10" is used to
deslocate the current number to the left, so the last digit can be setted...

This is a typical university exercise haha, I have mine one here yet,
but I quit the university in the same year =]

#include <stdio.h>

int main(int argc, char *argv[]){
int n, r = 0;

printf("\nentre com o numero: ");
scanf("%d", &n);

for(n = abs(n); n; r = r * 10 + n % 10, n /= 10);

printf("o inverso eh: %d", r);
return 0;
}


--
Jonas Raoni Soares Silva
http://www.jsfromhell.com

re: How do I "read-in" numbers from the left?

gk245 wrote:[color=blue]
> Sirius Black has brought this to us :[color=green]
>>
>> #include <stdio.h>
>>
>> int main (void)
>> {
>> int num = 0, revnum = 0, digit = 0;
>>
>> printf ("Enter a number: ");
>> scanf ("%i", &num);
>>
>> while (num > 0)
>> {
>> digit = num % 10;
>> revnum = revnum*10 + digit;
>> num /= 10;
>> }
>>
>> printf ("Reversed number is %d\n", revnum);
>> return 0;
>> }[/color]
>
> I might be reading this the wrong way, but if revnum is set to zero
> from the beginning, then revnum*10 will always equal zero. So the
> expression 'revnum = revnum*10 + digit' is just goint to set revnum to
> the digit's value..... i don't see why revnum*10 is needed since all
> its saying is that 0*10 + digit.[/color]


"Walk the code" with pen and paper, marking all changes of variables

code | num | revnum | digit |
------------------------+------+--------+-------+
initialization | 0 | 0 | 0 |
scanf | 4568 | 0 | 0 |
digit = num % 10 | 4568 | 0 | 8 |
revnum = ... | 4568 | 0*10+8 | 8 |
num /= 10 | 456 | 8 | 8 |
(loop)
digit = num % 10 | 456 | 8 | 6 |
revnum = ... | 456 | 8*10+6 | 6 |
num /= 10 | 45 | 86 | 6 |
(repeat ...) ... ... ...
printf | 0 | 8654 | 4 |
------------------------+------+--------+-------+

--
If you're posting through Google read <http://cfaj.freeshell.org/google>

re: How do I "read-in" numbers from the left?

Pedro Graca formulated on Wednesday :[color=blue]
> gk245 wrote:[color=green]
>> Sirius Black has brought this to us :[color=darkred]
>>>
>>> #include <stdio.h>
>>>
>>> int main (void)
>>> {
>>> int num = 0, revnum = 0, digit = 0;
>>>
>>> printf ("Enter a number: ");
>>> scanf ("%i", &num);
>>>
>>> while (num > 0)
>>> {
>>> digit = num % 10;
>>> revnum = revnum*10 + digit;
>>> num /= 10;
>>> }
>>>
>>> printf ("Reversed number is %d\n", revnum);
>>> return 0;
>>> }[/color]
>>
>> I might be reading this the wrong way, but if revnum is set to zero
>> from the beginning, then revnum*10 will always equal zero. So the
>> expression 'revnum = revnum*10 + digit' is just goint to set revnum to
>> the digit's value..... i don't see why revnum*10 is needed since all
>> its saying is that 0*10 + digit.[/color]
>
>
> "Walk the code" with pen and paper, marking all changes of variables
>
> code | num | revnum | digit |
> ------------------------+------+--------+-------+
> initialization | 0 | 0 | 0 |
> scanf | 4568 | 0 | 0 |
> digit = num % 10 | 4568 | 0 | 8 |
> revnum = ... | 4568 | 0*10+8 | 8 |
> num /= 10 | 456 | 8 | 8 |
> (loop)
> digit = num % 10 | 456 | 8 | 6 |
> revnum = ... | 456 | 8*10+6 | 6 |
> num /= 10 | 45 | 86 | 6 |
> (repeat ...) ... ... ...
> printf | 0 | 8654 | 4 |
> ------------------------+------+--------+-------+[/color]

doh...i forgot that it was adding the digit, was just looking at revnum
= revnum * 10.

Thanks, i like the table approach. Will use it quite a bit, i am sure.

^^

re: How do I "read-in" numbers from the left?

On Tue, 21 Feb 2006 05:38:56 +0200, "stathis gotsis"
<stathisgotsis@hotmail.com> wrote:
[color=blue]
> I do not know if you are "allowed" this but anyway take a look, printdec()
> is recursive:
>
> #include <stdio.h>
>
> void printdec(unsigned int i)
> {
> if (i/10) printdec(i/10);
> printf("%d",i%10);
> fflush(stdout);
> }
>[/color]
If you have printf (with %u or probably %d) you don't need your
recursive logic. But all you need is putchar ('0' + i%10).

Doing the fflush() for each digit is probably wasteful.
[color=blue]
> int main(void)
> {
> unsigned int number;
>
> printf("Enter numbers: ");
> scanf ("%d", &number);
>[/color]
#if stdclc
Prompt not ending with newline (and perhaps even with) is not strictly
guaranteed to appear if you don't fflush(stdout).

%d is technically incorrect for unsigned int, use %u.
Or use an int variable; it will converted on the call next.
#endif
[color=blue]
> printdec(number);
> printf("\n");[/color]

This could also be a putchar ('\n').
[color=blue]
>
> return 0;
> }
>
> It can print non-negative numbers in their decimal representation.
> I tried to keep your own code too, even if it is not that safe. You can work
> out the rest.
>[/color]

- David.Thompson1 at worldnet.att.net