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scanf problem

I know this is the problem that most newbies get into.

#include<stdio. h>
int main(void)
{
char a;
scanf("%c",&a); /*1st scanf */
printf("%c\n",a );
scanf("%c",&a); /*2nd scanf*/
printf("%c\n",a );
return 0;
}

This will not work, because after the first scanf a newline is left
behind in the input stream, unconsumed.

I made this attempt to solve this problem

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c",&a);
printf("%c\n",a );
getchar(); /* putting getc(stdin) also worked*/
scanf("%c",&a);
printf("%c\n",a );
return 0;
}

Out of curiosity I tried this also,

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c",&a);
printf("%c\n",a );
scanf("\n%c",&a );
printf("%c\n",a );
return 0;
}

which gave me expected output.

But my question is (finally!) , why the following code doesn't work,

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c\n",&a ); /* 1st scanf */
printf("%c\n",a );
scanf("%c",&a); /* 2nd scanf */
printf("%c\n",a );
return 0;
}

My assumption was 1st scanf will consume the newline left in the input
stream.
Thanks for your time,
Yugi.

Sep 8 '06 #1
14 13842
I use fscanf to read from a file and the newline is consumed, using
both MS-VC 6 and gcc 3.3.5. What are you using?

Sep 8 '06 #2
main() wrote:
I know this is the problem that most newbies get into.

#include<stdio. h>
int main(void)
{
char a;
scanf("%c",&a); /*1st scanf */
printf("%c\n",a );
scanf("%c",&a); /*2nd scanf*/
printf("%c\n",a );
return 0;
}

This will not work, because after the first scanf a newline is left
behind in the input stream, unconsumed.

I made this attempt to solve this problem

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c",&a);
printf("%c\n",a );
getchar(); /* putting getc(stdin) also worked*/
scanf("%c",&a);
printf("%c\n",a );
return 0;
}
This will only work (the way you seem to want it to) if the second
character in the first input line is a newline. You introduced a new
variable here, b, did you mean to do something with it?
Out of curiosity I tried this also,

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c",&a);
printf("%c\n",a );
scanf("\n%c",&a );
printf("%c\n",a );
return 0;
}

which gave me expected output.
Any whitespace in the format string will match any amount of whitespace
in the input, including none. Your newline will match any number of
spaces, tabs, newlines, etc., until a non-whitespace character is
encountered.
But my question is (finally!) , why the following code doesn't work,

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c\n",&a ); /* 1st scanf */
printf("%c\n",a );
scanf("%c",&a); /* 2nd scanf */
printf("%c\n",a );
return 0;
}

My assumption was 1st scanf will consume the newline left in the input
stream.
The first scanf call will store the first character into a and consume
of any immediately following whitespace (including newlines and any
whitespace that follows). You didn't specify what the input was that
you used or how the output differed from your expectations, so it's
difficult to help you understand what the "problem" is, feel free to
clarify.

See also my response to the thread entitled "cannot use char and
integer in the same program" on August 10th 2006 in this group.

Robert Gamble

Sep 8 '06 #3

Robert Gamble wrote:
main() wrote:
I know this is the problem that most newbies get into.

#include<stdio. h>
int main(void)
{
char a;
scanf("%c",&a); /*1st scanf */
printf("%c\n",a );
scanf("%c",&a); /*2nd scanf*/
printf("%c\n",a );
return 0;
}

This will not work, because after the first scanf a newline is left
behind in the input stream, unconsumed.

I made this attempt to solve this problem

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c",&a);
printf("%c\n",a );
getchar(); /* putting getc(stdin) also worked*/
scanf("%c",&a);
printf("%c\n",a );
return 0;
}

This will only work (the way you seem to want it to) if the second
character in the first input line is a newline. You introduced a new
variable here, b, did you mean to do something with it?
Out of curiosity I tried this also,

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c",&a);
printf("%c\n",a );
scanf("\n%c",&a );
printf("%c\n",a );
return 0;
}

which gave me expected output.

Any whitespace in the format string will match any amount of whitespace
in the input, including none. Your newline will match any number of
spaces, tabs, newlines, etc., until a non-whitespace character is
encountered.
But my question is (finally!) , why the following code doesn't work,

#include<stdio. h>
int main(void)
{
char a,b;
scanf("%c\n",&a ); /* 1st scanf */
printf("%c\n",a );
scanf("%c",&a); /* 2nd scanf */
printf("%c\n",a );
return 0;
}

My assumption was 1st scanf will consume the newline left in the input
stream.

The first scanf call will store the first character into a and consume
of any immediately following whitespace (including newlines and any
whitespace that follows). You didn't specify what the input was that
you used or how the output differed from your expectations, so it's
difficult to help you understand what the "problem" is, feel free to
clarify.
Hi,

for the last code snippet
this is the output i got

y
z
y
z

when i entered y , it didn't print anything
when i entered z, it printed both y and z.
What i expected is this,

y
y
z
z

Thanks for your time,
Yugi.

Sep 8 '06 #4
To solve this problem i modified the code as follows:

#include<stdio. h>
main(void)
{
char a;
flushall();
//scanf("%c\n",&a ); /* 1st scanf */
a=getchar();
printf("%c\n",a );
scanf("%c",&a); /* 2nd scanf */
printf("%c\n",a );
return 0;

}
but here i found more interesting part as, it does not stop for getting
input for 2nd scanf statement. Can someone , why??????????

Sep 8 '06 #5
"Shashank" <sm*******@gmai l.comwrites:
To solve this problem i modified the code as follows:

#include<stdio. h>
main(void)
{
char a;
flushall();
//scanf("%c\n",&a ); /* 1st scanf */
a=getchar();
printf("%c\n",a );
scanf("%c",&a); /* 2nd scanf */
printf("%c\n",a );
return 0;

}
What is flushall()? There is no such function in standard C. What is
it supposed to do?

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
Sep 8 '06 #6
>
What is flushall()? There is no such function in standard C. What is
it supposed to do?
flushall(); flushes the buffer to aviod the entry of garbage values.

Sep 8 '06 #7
Shashank said:
>
>>
What is flushall()? There is no such function in standard C. What is
it supposed to do?

flushall(); flushes the buffer to aviod the entry of garbage values.
On your system, perhaps it does; but the C Standard does not guarantee this.
On some other system, it might do something else entirely.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)
Sep 8 '06 #8
There is NO flushall() function.

There is one function fflush(), which flushes out the i/o stream data.

Richard Heathfield wrote:
Shashank said:
>
What is flushall()? There is no such function in standard C. What is
it supposed to do?
flushall(); flushes the buffer to aviod the entry of garbage values.

On your system, perhaps it does; but the C Standard does not guarantee this.
On some other system, it might do something else entirely.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)
Sep 8 '06 #9
Ratan said:
There is NO flushall() function.
Correction: the C standard library does not provide one. Implementation
providers are free to provide a function by that name in a third-party
library if they choose, and at least one such provider does precisely that.
There is one function fflush(), which flushes out the i/o stream data.
Indeed - and fflush(NULL) flushes out /all/ data currently pending on
streams open for output or update. This is guaranteed by the Standard.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)
Sep 8 '06 #10

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