echo charecter program...

[hdsalbki]

hi everyone,
I have below a small program to echo back what character the user
types. It's working OK but prints a extra prompt between every
character. what can I do? I'm new in C and my book is very
difficult...
thanks for any help.

#include<stdio. h>

main()
{
char a;
while(1)
{
printf("\nPleas e type a character: ");
scanf("%c",&a);
printf("\nYou typed: %c",a);
}
}

[CBFalconer]

hdsalbki wrote:

CBFalconer wrote:

.... snip ...

>

>for example:

do {
/* something that eats chars other than '\n' */
} while (EOF != flushln(stdin)) ;

Thanks CBFalconer. But when I run the following program which uses
your code, I can't get past the first prompt. The app just seems to
there and all I can do is kill it with ctrl-c. Am I doing something
wrong? I copies and pasted your code so to avoid typo...

#include <stdio.h>

int flushln(FILE *f) {
int ch;
while ((EOF != (ch = getc(f))) || (ch != '\n')) continue;
return ch;
} /* flushln */

That || should be a && ------------^ Sorry.

>
int main(void)
{
char a;
while(1)
{
printf("Please enter a character: ");
fflush(stdout);
scanf("%c",&a);
printf("You typed: %c\n",a);
flushln(stdin);
}
return 0;
}

o/p is:

dodo@sapphire:~/src/c/ws$ ./echo_char3
Please enter a character: x
You typed: x

Program hangs here. whatever I type the prompt is not printing again.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

[lawrence.jones]

Keith Thompson <ks***@mib.orgw rote:

>
For an unbuffered stream, output appears immediately. For a line
buffered stream, it appears only when a line has been completed.

Not quite -- it is also supposed to appear when the buffer is full
(obviously), when input is requested on an unbuffered stream, and when
input is requested on a line buffered stream whose buffer is empty.

If standard output is going to an interactive device, such as a
terminal or emulator, it's required to be either unbuffered or line
buffered.

Provided the implementation can determine that it *is* an interactive
device. It's not always possible.

If it's line buffered, you need the call to fflush(stdout)
to force a partial line to appear. *However*, on most modern systems,
standard output for an interactive program is likely to be unbuffered,
which means that fflush(stdout) will have no effect.

Actually, most modern system line buffer interactive devices by default
for both input and output, so the above rules make the fflush()
redundant. However:

Adding the
fflush(stdout) is a precaution that may not be necessary for your
system, but it is necessary if you want your program to be maximally
portable.

That is 100% correct!
--
Larry Jones

I'm so disappointed. -- Calvin

[Walter Roberson]

In article <1v************ @jones.homeip.n et>,
<la************ @siemens.comwro te:

>Keith Thompson <ks***@mib.orgw rote:

>For an unbuffered stream, output appears immediately. For a line
buffered stream, it appears only when a line has been completed.

>Not quite -- it is also supposed to appear when the buffer is full
(obviously), when input is requested on an unbuffered stream, and when
input is requested on a line buffered stream whose buffer is empty.

Hmmm, traditionally switching from output to input required
an explicit fseek() call; did that change in C99?
--
"There are some ideas so wrong that only a very intelligent person
could believe in them." -- George Orwell

[Keith Thompson]

la************@ siemens.com writes:

Keith Thompson <ks***@mib.orgw rote:

>>
For an unbuffered stream, output appears immediately. For a line
buffered stream, it appears only when a line has been completed.

Not quite -- it is also supposed to appear when the buffer is full
(obviously), when input is requested on an unbuffered stream, and when
input is requested on a line buffered stream whose buffer is empty.

Hey, you don't expect me to cover *everything*, do you? 8-)}

>If standard output is going to an interactive device, such as a
terminal or emulator, it's required to be either unbuffered or line
buffered.

Provided the implementation can determine that it *is* an interactive
device. It's not always possible.

But implementations are effectively required to assume that the device
is interactive if they can't prove it isn't. C99 7.19.3p7:

As initially opened, the standard error stream is not fully
buffered; the standard input and standard output streams are fully
buffered if and only if the stream can be determined not to refer
to an interactive device.

>If it's line buffered, you need the call to fflush(stdout)
to force a partial line to appear. *However*, on most modern systems,
standard output for an interactive program is likely to be unbuffered,
which means that fflush(stdout) will have no effect.

Actually, most modern system line buffer interactive devices by default
for both input and output, so the above rules make the fflush()
redundant. However:

Ah, I see. Line-buffering is sufficient because the input request
causes the partial line to appear. Whereas if I write:

printf("Hello, ");
/* something that takes a long time */
printf("world\n ");

the line "Hello, world" will be printed all at once after a delay.

>Adding the
fflush(stdou t) is a precaution that may not be necessary for your
system, but it is necessary if you want your program to be maximally
portable.

--
Keith Thompson (The_Other_Keit h) 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"

[lawrence.jones]

Walter Roberson <ro******@ibd.n rc-cnrc.gc.cawrote :

In article <1v************ @jones.homeip.n et>,
<la************ @siemens.comwro te:

Not quite -- it is also supposed to appear when the buffer is full
(obviously), when input is requested on an unbuffered stream, and when
input is requested on a line buffered stream whose buffer is empty.

Hmmm, traditionally switching from output to input required
an explicit fseek() call; did that change in C99?

No, but the above is talking about input on *any* stream, not just the
same stream, so that's not really relevant.
--
Larry Jones

All this was funny until she did the same thing to me. -- Calvin

[lawrence.jones]

Keith Thompson <ks***@mib.orgw rote:

>
But implementations are effectively required to assume that the device
is interactive if they can't prove it isn't. C99 7.19.3p7:

Actually, 7.19.5.3p7 is the better reference, since it applies to all
streams, not just stdout and stderr. (I misremembered the requirement
and thought it went the other way.)

Ah, I see. Line-buffering is sufficient because the input request
causes the partial line to appear. Whereas if I write:

printf("Hello, ");
/* something that takes a long time */
printf("world\n ");

the line "Hello, world" will be printed all at once after a delay.

Correct on both counts.
--
Larry Jones

Archaeologists have the most mind-numbing job on the planet. -- Calvin