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[ques]use recursive function to print out n!

P: n/a
this is my C Programming homework,

It wants me to input 10! and output the follow result

10!

10 * 9!

9 * 8!
..................
2* 1!

1

I take it for decreasing by degress, so using two for() loop to execute..
but I spend two days to try and can not figure out what the problem is.

Could anybody show me a hint with this ? thank you so much.

I use the compiler with dec C++ to finish the C programming follow
----------------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>

long fact(int num);
int main(void)
{
int i,j; /* counter */
int ans = 1;
printf("Input the n!:");
scanf("%d", &i);

for(i=10;i>=1;i--)
{
for(j=9;j>=0;j--)
{
ans *= j;
printf("%d * %2d! = %d\n",i, j, i*j );

}
printf("\n");
}
system("pause");
return 0;
}
/* Recursive fonction */
long fact(int num)
{
if(num<=1){
return 1;
}
else{
return (num * fact(num-1));
}
}

--
~wwww weiyu.csie.net  
xax  keith 
wwww o 140.120.238.173 
Nov 15 '05 #1
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10 Replies


P: n/a
AK
Hi

This is quite easy. You don't need 2 for-loops for that.

action! wrote:
this is my C Programming homework,

It wants me to input 10! and output the follow result

10!

10 * 9!

9 * 8!
..................
2* 1!

1

I take it for decreasing by degress, so using two for() loop to execute..
but I spend two days to try and can not figure out what the problem is.
Could anybody show me a hint with this ? thank you so much.


When you get questions like this, keep in mind that all the elements
need not be put in a single loop.
Some of them maybe formaing a series while others have to be done
seperately.
In your case, the first 10! can be done seperately. The rest forms a
series, as
10!, (10-1)!
9!, (9-1)!
.....
......
.........
1!,(1-1)!
Since you already have a recursive function to computer the factorial
of a number called fact(), you could use a single for loop to do the
series.

Hope you get the idea. If not, please feel free to contact me.

Regards
AK
Owner
Programmer's HQ
http://groups.google.com/group/programhq

Nov 15 '05 #2

P: n/a
ke*******@weiyu.csie.net (action!) writes:
this is my C Programming homework,

It wants me to input 10! and output the follow result

10!

10 * 9!

9 * 8!
..................
2* 1!

1

I take it for decreasing by degress, so using two for() loop to execute..
but I spend two days to try and can not figure out what the problem is.

Could anybody show me a hint with this ? thank you so much.
[snippet]


Basically, you don't need a "for" loop if you employ a recursive function like the "fact()"
defined in your code. Therefore, what you want is simply as follows:

--- begin here

#include <stdio.h>
#include <stdlib.h>

long fact(int num);
int main(void)
{
int i; /* counter */
printf("Input the n!:");
scanf("%d", &i);

fact(i);

}
/* Recursive fonction */
long fact(int num)
{
if(num<=1){
return 1;
}
else{
printf("%d!\n|\n%d x (%d-1)!\n", num, num, num);
return (num * fact(num-1));
}
}

--- end here

--
Denis H. G.
Nov 15 '05 #3

P: n/a
Denis H. G. wrote:
ke*******@weiyu.csie.net (action!) writes:
this is my C Programming homework,

It wants me to input 10! and output the follow result

10!

10 * 9!

9 * 8!
..................
2* 1!

1

I take it for decreasing by degress, so using two for() loop to execute...
but I spend two days to try and can not figure out what the problem is.

Could anybody show me a hint with this ? thank you so much.
[snippet]


Basically, you don't need a "for" loop if you employ a recursive functionlike the "fact()"
defined in your code. Therefore, what you want is simply as follows:

--- begin here

#include <stdio.h>
#include <stdlib.h>

long fact(int num);
int main(void)
{
int i; /* counter */
printf("Input the n!:");
scanf("%d", &i);

fact(i);

}
/* Recursive fonction */
long fact(int num)
{
if(num<=1){
return 1;
}
else{
printf("%d!\n|\n%d x (%d-1)!\n", num, num, num);
return (num * fact(num-1));
}
}

--- end here

--
Denis H. G.


I was also thinking the same thing. I did the following. HOWEVER,
scanf() still has to checked for 'funky input chars'. I had no idea how
to do this. I suppose I could have thought about it, but I was too
lazy.

-------------------ans.c--------------------------------------------------
#include <stdio.h>
#include <stdib.h>

int fact(int);

int fact(int num) {
if(num(<=1){
return 1;
}
else {
printf("%d! * %d! \n",num,num-1);
}

}

int main(void) {
int i = 0;
printf("Input the n! \n");
scanf("%d! \n", &i);
fact(i);
return 0;
}

-----------------------------------------------------------------------------

Chad

Nov 15 '05 #4

P: n/a
Chad wrote:
I was also thinking the same thing. I did the following. HOWEVER,
scanf() still has to checked for 'funky input chars'. I had no idea how
to do this. I suppose I could have thought about it, but I was too
lazy.
#include <stdio.h>
#include <stdib.h>

int main(void) {
int i = 0;
printf("Input the n! \n");
scanf("%d! \n", &i);
fact(i);
return 0;
}

$ man scanf:
`scanf' returns the number of input fields successfully scanned, con-
verted and stored; the return value does not include scanned fields
which were not stored.

=> Ans: check the return value is equal to one. Check the return values
of functions.

Check the return values of functions.

Note that if scanf stops scanning then the remaining characters on input
are still waiting to be read. So if scanf stops there will still be
input waiting and you have to worry about that if you want to read
anything else in. E.g. your format string will read the number entered,
but if the next character is not a '!' it will be left waiting on the
input buffer. Similarly for ' ' and '\n' after it. OTOH "%d%*s" will
pick up the number and eat the rest of the string until the end of the
input buffer.

Check the return values of functions.

--
imalone
Nov 15 '05 #5

P: n/a
AK
Hi
action! wrote:
this is my C Programming homework,

It wants me to input 10! and output the follow result

10!

10 * 9!

9 * 8!
..................
2* 1!

1
So, do you want to display this excactly the way it is written here??
If so, I misunderstood the program as I thought you need to compute
the value of each factorial.
I take it for decreasing by degress, so using two for() loop to execute..
but I spend two days to try and can not figure out what the problem is.

Could anybody show me a hint with this ? thank you so much.

I use the compiler with dec C++ to finish the C programming follow
----------------------------------------------------------------------------
I suppose you meant dev C++

<snipped>
/* Recursive fonction */
long fact(int num)
{
if(num<=1){
return 1;
}
else{
return (num * fact(num-1));
}
}


Why do you need this fact()?? This is a function to computer factorial
of a number. Actually, this is what made me misunderstand your
question.

What I see now, is that your assignment doesn't need recursion at all.
It can be simply done like this :
////////////////////////////////////////////
printf ( " \n 10! " ) ;

for ( i = 10; i > 1; i -- )
{ printf ( "\n %d * %d ! ", i, i-1 ) ;
/* I don't know how to print that arrow you have shown. So, replace
this comment
by the printf() for the arrow
*/

printf ( " \n 1 " ) ;
//////////////////////////////////////////////

If recursion is compulsory, here it goes :

////////////////////////////////////
printf ( " \n 10! " ) ;

fact ( ) ;

printf ( " \n 1 " ) ;
//////////////////////////////////////
void fact ( )
{ static int i = 10;
if ( i > 1 )
{
printf ( "\n %d * %d ! ", i, i-1 ) ;
/* I don't know how to print that arrow you have shown. So, replace
this comment
by the printf() for the arrow
*/
fact ( ) ;
}
}
///////////////////////////////////////

Regards
AK
Owner
Programmer's HQ
http://groups.google.com/group/programhq

Nov 15 '05 #6

P: n/a
AK

Chad wrote:
Denis H. G. wrote:
ke*******@weiyu.csie.net (action!) writes:
this is my C Programming homework,

It wants me to input 10! and output the follow result

10!

10 * 9!

9 * 8!
..................
2* 1!

1

I take it for decreasing by degress, so using two for() loop to execute..
but I spend two days to try and can not figure out what the problem is.

Could anybody show me a hint with this ? thank you so much.
[snippet]
Basically, you don't need a "for" loop if you employ a recursive function like the "fact()"
defined in your code. Therefore, what you want is simply as follows:

--- begin here

#include <stdio.h>
#include <stdlib.h>

long fact(int num);
int main(void)
{
int i; /* counter */
printf("Input the n!:");
scanf("%d", &i);

fact(i);

}
/* Recursive fonction */
long fact(int num)
{
if(num<=1){
return 1;
}
else{
printf("%d!\n|\n%d x (%d-1)!\n", num, num, num);
return (num * fact(num-1));
}
}

--- end here

--
Denis H. G.


I was also thinking the same thing. I did the following. HOWEVER,
scanf() still has to checked for 'funky input chars'. I had no idea how
to do this. I suppose I could have thought about it, but I was too
lazy.


In case you still have no idea how to do it, please visit
http://groups.google.com/group/programhq and check out "More I/O
Stream" thread. I have posted the code for checking 'funky input chars'
in case of inputting integers.
-------------------ans.c--------------------------------------------------
#include <stdio.h>
#include <stdib.h>

int fact(int);

int fact(int num) {
if(num(<=1){
return 1;
}
else {
printf("%d! * %d! \n",num,num-1);
}

}

int main(void) {
int i = 0;
printf("Input the n! \n");
scanf("%d! \n", &i);
fact(i);
return 0;
}

-----------------------------------------------------------------------------

Chad


Nov 15 '05 #7

P: n/a
AK wrote:
Chad wrote:
Denis H. G. wrote:
ke*******@weiyu.csie.net (action!) writes:

> this is my C Programming homework,
>
> It wants me to input 10! and output the follow result
>
> 10!
> ↓
> 10 * 9!
> ↓
> 9 * 8!
> ..................
> 2* 1!
> ↓
> 1
>
> I take it for decreasing by degress, so using two for() loop to execute..
> but I spend two days to try and can not figure out what the problemis.
>
> Could anybody show me a hint with this ? thank you so much.
> [snippet]

Basically, you don't need a "for" loop if you employ a recursive function like the "fact()"
defined in your code. Therefore, what you want is simply as follows:

--- begin here

#include <stdio.h>
#include <stdlib.h>

long fact(int num);
int main(void)
{
int i; /* counter */
printf("Input the n!:");
scanf("%d", &i);

fact(i);

}
/* Recursive fonction */
long fact(int num)
{
if(num<=1){
return 1;
}
else{
printf("%d!\n|\n%d x (%d-1)!\n", num, num, num);
return (num * fact(num-1));
}
}

--- end here

--
Denis H. G.


I was also thinking the same thing. I did the following. HOWEVER,
scanf() still has to checked for 'funky input chars'. I had no idea how
to do this. I suppose I could have thought about it, but I was too
lazy.


In case you still have no idea how to do it, please visit
http://groups.google.com/group/programhq and check out "More I/O
Stream" thread. I have posted the code for checking 'funky input chars'
in case of inputting integers.
-------------------ans.c--------------------------------------------------
#include <stdio.h>
#include <stdib.h>

int fact(int);

int fact(int num) {
if(num(<=1){
return 1;
}
else {
printf("%d! * %d! \n",num,num-1);
}

}

int main(void) {
int i = 0;
printf("Input the n! \n");
scanf("%d! \n", &i);
fact(i);
return 0;
}

-----------------------------------------------------------------------------

Chad

Hmmm.... I noticed I forget a line on the fact() function. I guess that
is what I get for typing it in vs copying and pasting actual working
code. The fact() I meant to use use was

int fact(int num) {
if(num(<=1){
return 1;
}
else {
printf("%d! * %d! \n",num,num-1);
fact(num-1); /*line I forget in the original code -( */
}

}
With that out of my system, I will just wander over to the link you
posted and read it. If I become too dense when I read it, I'll post my
confusion in the proper forum.

Chad

Nov 15 '05 #8

P: n/a
AK
Hi Chad

Chad wrote:
AK wrote:
Chad wrote:
Denis H. G. wrote:
> ke*******@weiyu.csie.net (action!) writes:
>
> > this is my C Programming homework,
> >
> > It wants me to input 10! and output the follow result
> >
> > 10!
> > ↓
> > 10 * 9!
> > ↓
> > 9 * 8!
> > ..................
> > 2* 1!
> > ↓
> > 1
> >
> > I take it for decreasing by degress, so using two for() loop to execute..
> > but I spend two days to try and can not figure out what the problem is.
> >
> > Could anybody show me a hint with this ? thank you so much.
> > [snippet]
>
> Basically, you don't need a "for" loop if you employ a recursive function like the "fact()"
> defined in your code. Therefore, what you want is simply as follows:
>
> --- begin here
>
> #include <stdio.h>
> #include <stdlib.h>
>
> long fact(int num);
> int main(void)
> {
> int i; /* counter */
> printf("Input the n!:");
> scanf("%d", &i);
>
> fact(i);
>
> }
> /* Recursive fonction */
> long fact(int num)
> {
> if(num<=1){
> return 1;
> }
> else{
> printf("%d!\n|\n%d x (%d-1)!\n", num, num, num);
> return (num * fact(num-1));
> }
> }
>
> --- end here
>
> --
> Denis H. G.

I was also thinking the same thing. I did the following. HOWEVER,
scanf() still has to checked for 'funky input chars'. I had no idea how
to do this. I suppose I could have thought about it, but I was too
lazy.


In case you still have no idea how to do it, please visit
http://groups.google.com/group/programhq and check out "More I/O
Stream" thread. I have posted the code for checking 'funky input chars'
in case of inputting integers.
-------------------ans.c--------------------------------------------------
#include <stdio.h>
#include <stdib.h>

int fact(int);

int fact(int num) {
if(num(<=1){
return 1;
}
else {
printf("%d! * %d! \n",num,num-1);
}

}

int main(void) {
int i = 0;
printf("Input the n! \n");
scanf("%d! \n", &i);
fact(i);
return 0;
}

-----------------------------------------------------------------------------

Chad

Hmmm.... I noticed I forget a line on the fact() function. I guess that
is what I get for typing it in vs copying and pasting actual working
code. The fact() I meant to use use was

int fact(int num) {
if(num(<=1){
return 1;
}
else {
printf("%d! * %d! \n",num,num-1);
fact(num-1); /*line I forget in the original code -( */
}

}
With that out of my system, I will just wander over to the link you
posted and read it. If I become too dense when I read it, I'll post my
confusion in the proper forum.

proper forum?????????

Regards
AK

Nov 15 '05 #9

P: n/a
Hmmm.... I noticed I forget a line on the fact() function. I guess that
is what I get for typing it in vs copying and pasting actual working
code. The fact() I meant to use use was

int fact(int num) {
if(num(<=1){
return 1;
}
else {
printf("%d! * %d! \n",num,num-1);
fact(num-1); /*line I forget in the original code -( */
}

}
With that out of my system, I will just wander over to the link you
posted and read it. If I become too dense when I read it, I'll post my
confusion in the proper forum.

proper forum?????????

Regards
AK


Well, I was thinking that I wouldn't post a question about scanf() in
say alt.fetish.tongue. Okay, I have managed to wander totally off
topic.

Chad

Nov 15 '05 #10

P: n/a
On Mon, 07 Nov 2005 13:58:11 +0000, Ian Malone <ib***@cam.ac.uk>
wrote:
> scanf("%d! \n", &i);
=> Ans: check the return value is equal to one. Check the return values
of functions.

Check the return values of functions.
Right. (Twice.)
Note that if scanf stops scanning then the remaining characters on input
are still waiting to be read. So if scanf stops there will still be
input waiting and you have to worry about that if you want to read
anything else in. E.g. your format string will read the number entered,
but if the next character is not a '!' it will be left waiting on the
Right.
input buffer. Similarly for ' ' and '\n' after it.
Wrong. Any whitespace in a *scanf format matches not just that
specific character but _all_ consecutive whitespace in the input.
Thus the ' ' can match and "use up" say several newlines and several
leading spaces, stopping only at the next "printing" character (or EOF
including end-of-string or error). FAQ 12.17 at the usual places and
http://www.eskimo.com/~scs/C-faq/top.html .
OTOH "%d%*s" will
pick up the number and eat the rest of the string until the end of the
input buffer.
%s matches, and %*s discards, only upto whitespace (or end).

%*[^\n] discards up to newline, which will often probably usually be
the same as an "input buffer" but not always.
Check the return values of functions.


Still right. :-)
- David.Thompson1 at worldnet.att.net
Nov 15 '05 #11

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