Why is it wrong??(About n!)

[upyzl]

I want to calculate n!,and my C code is as follows:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int nonnega_int, counter;
unsigned long result = 1;

printf("Enter a nonnegative integer (as n)\n");
printf("and I'll calculate its factorial(EOF to end):\n");
scanf("%d", &nonnega_int);

while ( ( nonnega_int = getchar() ) != EOF ){
if ( nonnega_int 0){
for ( counter = 1; counter <= nonnega_int; counter++){
result *= counter;
}
}

else if ( nonnega_int = 0)
result = 0;

printf("n! = %lu\n", result);
}

system("pause");

return 0;
}
but the result is always 3628800
I don't know why it is wrong.
Please help me check it out.

[Ben Bacarisse]

upyzl <zj******@163.comwrites:

I want to calculate n!,and my C code is as follows:

I'd expect to see a factorial function but maybe you haven't covered
functions yet.

#include <stdio.h>
#include <stdlib.h>
int main()
{
int nonnega_int, counter;
unsigned long result = 1;

printf("Enter a nonnegative integer (as n)\n");
printf("and I'll calculate its factorial(EOF to end):\n");
scanf("%d", &nonnega_int);

You should check the result of this call.

while ( ( nonnega_int = getchar() ) != EOF ){

However, now you assign nonnega_int after having just read a number
into it. The result of the getchar() call is not what you want to
calculate the factorial of.

What is the point of the while loop?

if ( nonnega_int 0){
for ( counter = 1; counter <= nonnega_int; counter++){
result *= counter;
}
}

else if ( nonnega_int = 0)

You meant == not =. Many people like to write these test the otehr
way round (0 == nonnega_int) so you get a diagnostic when you misspell
==. Personally, I hate it, but then its years since I've made this
particular mistake.

result = 0;

printf("n! = %lu\n", result);
}

system("pause");

There must be a better way to see your output!

return 0;
}

--
Ben.

[Pilcrow]

On Wed, 29 Oct 2008 19:15:01 -0700 (PDT), upyzl <zj******@163.com>
wrote:

>I want to calculate n!,and my C code is as follows:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int nonnega_int, counter;
unsigned long result = 1;

printf("Enter a nonnegative integer (as n)\n");
printf("and I'll calculate its factorial(EOF to end):\n");
scanf("%d", &nonnega_int);

while ( ( nonnega_int = getchar() ) != EOF ){
if ( nonnega_int 0){
for ( counter = 1; counter <= nonnega_int; counter++){
result *= counter;
}
}

else if ( nonnega_int = 0)
result = 0;

printf("n! = %lu\n", result);
}

system("pause");

return 0;
}
but the result is always 3628800
I don't know why it is wrong.
Please help me check it out.

notice that 10! = 3628800, which is your invariable result.

[Keith Thompson]

upyzl <zj******@163.comwrites:

I want to calculate n!,and my C code is as follows:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int nonnega_int, counter;
unsigned long result = 1;

printf("Enter a nonnegative integer (as n)\n");
printf("and I'll calculate its factorial(EOF to end):\n");
scanf("%d", &nonnega_int);

Here you read an int value from stdin, storing it in nonnega_int.

while ( ( nonnega_int = getchar() ) != EOF ){

And here you clobber whatever value you just stored in nonnega_int,
replacing it with the value of the next character read from stdin. If
the next character happens to be a new-line ('\n'), and if the value
of '\n' happens to be 10 on your system (which it almost certainly
is), then you compute '\n'!.

Presumably you want to read a sequence of integer values. Why do you
have a loop reading individual characters?

[snip]

--
Keith Thompson (The_Other_Keith) ks***@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"

[upyzl]

Now I change it into:

#include <stdio.h>
#include <stdlib.h>
int main()
{
int nonnega_int, counter;
unsigned long result = 1;

printf("Enter a nonnegative integer\n");
printf("and I'll calculate its factorial(EOF to end):\n");
scanf("%d", &nonnega_int);

while ( ( nonnega_int = getchar() ) != EOF ){
if ( nonnega_int 0){
for ( counter = 1; counter <= nonnega_int; counter++){
result *= counter;
}
}
else if ( nonnega_int < 0){
printf("Error Input\n");
}
printf("%d! = %lu\n", nonnega_int, result);
}

system("pause");

return 0;
}

I know that now my only problem is "while ( ( nonnega_int =
getchar() ) != EOF )"
but I want to loop as what user want.
Should I add "int loop" or?

I must say, I haven't studied about "goto" and of course I don't know
how to use it.
In fact, now I only know use "while ( ( XXXX = getchar() ) != EOF )"
to control loop times,
and I think it should work.

What should I do?

[upyzl]

Now I change it into:

#include <stdio.h>
#include <stdlib.h>
int main()
{
int nonnega_int, counter;
unsigned long result = 1;
printf("Enter a nonnegative integer\n");
printf("and I'll calculate its factorial(EOF to end):\n");
scanf("%d", &nonnega_int);
while ( ( nonnega_int = getchar() ) != EOF ){
if ( nonnega_int 0){
for ( counter = 1; counter <= nonnega_int;
counter++){
result *= counter;
}
}
if ( nonnega_int == 0){
result = 1;
}
else {
printf("Error Input\n");
}
printf("%d! = %lu\n", nonnega_int, result);
}
system("pause");
return 0;

}
I know that now my only problem is "while ( ( nonnega_int =
getchar() ) != EOF )"
but I want to loop as what user want.
Should I add "int loop" or?

I must say, I haven't studied about "goto" and of course I don't know
how to use it.
In fact, now I only know use "while ( ( XXXX = getchar() ) != EOF )"
to control loop times,
and I think it should work.
What should I do?

[upyzl]

Now I change it into:

#include <stdio.h>
#include <stdlib.h>
int main()
{
int nonnega_int, counter;
unsigned long result = 1;
printf("Enter a nonnegative integer\n");
printf("and I'll calculate its factorial(EOF to end):\n");
scanf("%d", &nonnega_int);
while ( ( nonnega_int = getchar() ) != EOF ){
if ( nonnega_int 0){
for ( counter = 1; counter <=
nonnega_int;counter++){
result *= counter;
}
}
else if ( nonnega_int == 0){
result = 1;
}
else {
printf("Error Input\n");
}
printf("%d! = %lu\n", nonnega_int, result);
}
system("pause");
return 0;

}
I know that now my only problem is "while ( ( nonnega_int =
getchar() ) != EOF )"
but I want to loop as what user want.
Should I add "int loop" or?

I must say, I haven't studied about "goto" and of course I don't know
how to use it.
In fact, now I only know use "while ( ( XXXX = getchar() ) != EOF )"
to control loop times,
and I think it should work.
What should I do?

[Mark McIntyre]

upyzl wrote:

I want to calculate n!,and my C code is as follows:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int nonnega_int, counter;
unsigned long result = 1;

printf("Enter a nonnegative integer (as n)\n");
printf("and I'll calculate its factorial(EOF to end):\n");
scanf("%d", &nonnega_int);

don't use scanf. See hte C FAQ for why.

while ( ( nonnega_int = getchar() ) != EOF ){

You just read something into nonnega_int, and now you're overwriting it
with the retirn from getchar...

if ( nonnega_int 0){
for ( counter = 1; counter <= nonnega_int; counter++){

in C, the normal idiom is to start from zero, not one. You /can/ start
from one, but your code will be potentially confusing to others and
you'll run into problems when you start using arrays.

but the result is always 3628800

Check the value of nonnega_int immediately before you enter the 'for' loop.

--
Mark McIntyre

CLC FAQ <http://c-faq.com/>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt>

[Fred]

On Oct 30, 6:54*am, Mark McIntyre <[e-mail]>
wrote:

upyzl wrote:

I want to calculate n!,and my C code is as follows:

#include <stdio.h>
#include <stdlib.h>
int main()
{
* *int nonnega_int, counter;
* *unsigned long result = 1;

* *printf("Enter a nonnegative integer (as n)\n");
* *printf("and I'll calculate its factorial(EOF to end):\n");
* *scanf("%d", &nonnega_int);

don't use scanf. See hte C FAQ for why.

** while ( ( nonnega_int = getchar() ) != EOF ){

You just read something into nonnega_int, and now you're overwriting it
with the retirn from getchar...

* * * * * *if ( nonnega_int 0){
* * * * * * * * * *for ( counter = 1; counter <= nonnega_int; counter++){

in C, the normal idiom is to start from zero, not one. *You /can/ start
from one, but your code will be potentially confusing to others and
you'll run into problems when you start using arrays.

but the result is always 3628800

Check the value of nonnega_int immediately before you enter the 'for' loop.

And unless the value of "result" is reset to one before entering
the for-loop, only the first time can produce the desired answer.
--
Fred Kleinschmidt

[user923005]

On Oct 29, 7:15*pm, upyzl <[e-mail]:

I want to calculate n!,and my C code is as follows:

[snip]
Since the useful domain is very small for any native C data type, use
a table.
On a system with 128 bit floating point, there are still less than
2000 entries in the table.

If you are calculating n! to do probability studies, then I suggest
creation of Pascal's triangle and storing that.
Then all of your calculations are simple lookups.