Wierd output instead of 0s and 1s

[Sathyaish]

A practice excercise from K&R. Kindly read the comments within the
program. I'd be very grateful to people who helped. Why is it that I
get the wierd face-like characters on the screen instead of the
boolean output 0s or 1s?

#include <stdio.h>

/*This program is made to check that leaving the brackets around the
epxression (c=getchar()) in
the statement while ((c=getchar()) !=EOF) produces a boolean output in
C which would either be
0 (false) or 1 (true). This would happen because the relational
operator != has precedence over the assignment
operator =.
*/

void main()
{

int c;

while (c=getchar() != EOF) putchar(c);

/* Surprisingly, it doesn't produce zeros while I type; rather it
produces some wierd characters that look
half like zeros and half like smileys. And doing a Ctrl+Z, which I
thought was the substitute for EOF does
not produce a 1 (true value) */

}

 

[Joona I Palaste]

A practice excercise from K&R. Kindly read the comments within the
program. I'd be very grateful to people who helped. Why is it that I
get the wierd face-like characters on the screen instead of the
boolean output 0s or 1s?

Because 0 and 1 are not the same thing as '0' and '1'. Your program
is printing the characters whose character code is 0 and 1, not the
characters '0' and '1' themselves.

#include <stdio.h>

/*This program is made to check that leaving the brackets around the
epxression (c=getchar()) in
the statement while ((c=getchar()) !=EOF) produces a boolean output in
C which would either be
0 (false) or 1 (true). This would happen because the relational
operator != has precedence over the assignment
operator =.
*/

void main()

Non-standard form of main(). Better would be int main(void).

{

int c;

while (c=getchar() != EOF) putchar(c);

/* Surprisingly, it doesn't produce zeros while I type; rather it
produces some wierd characters that look
half like zeros and half like smileys. And doing a Ctrl+Z, which I
thought was the substitute for EOF does
not produce a 1 (true value) */

Note that if c==EOF, the putchar(c) is never called, so your program
will never print a 1 (true value) for any input.

 

[Joona I Palaste]

Non-standard form of main(). Better would be int main(void).

This loop is printing the character whose code is 1 (true value)
as long as getchar()!=EOF. Note that 1 and '1' are not the same thing.

Note that if c==EOF, the putchar(c) is never called, so your program
will never print a 1 (true value) for any input.

I meant, of course, "if getchar()==EOF and therefore c==0, the
putchar(c) is never called, so your program will never print a 0 (false
value) for any input."

--
/-- Joona Palaste ([email protected]) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Outside of a dog, a book is a man's best friend. Inside a dog, it's too dark
to read anyway."
- Groucho Marx

 

[Mark L Pappin]

(e-mail address removed) (Sathyaish) writes:

[rearranging for context]

#include <stdio.h>
void main() {
int c;
while (c=getchar() != EOF) putchar(c);

Why is it that I get the wierd face-like characters on the screen
instead of the boolean output 0s or 1s?

short:
Probably because '0' != 0 and '1' != 1, but maybe because 'void
main()' invokes undefined behaviour.


longer:
You call putchar() with the result of the comparison, which is indeed
0 or 1. On your platform (and the IBM PC BIOS uses this mapping),
characters 0 and 1 are smiley faces. If instead you use
putchar('0'+c)
you should see some of the results you expect.

Note that 'void main()' is not correct. Main must return int, or
anything at all is allowed to happen - the fact that things seem to
behave fairly normally is only one possible interpretation of
'anything at all'.


mlp

 

[Sathyaish]

Thank you so very much, Joona Palaste. Yeah, I realize I flipped the
zeros and ones in writing the original post.

You're de man!

Kind Regards,
Sathyaish Chakravarthy.