A trick with if-else

[Piyush Agarwal]

void main
{
int x;
if(x)
printf("Hello");
else
printf("World");
}
What value can be given to x such that the output is "Hello
World"?

 

[Vladimir Oka]

void main
{
int x;
if(x)
printf("Hello");
else
printf("World");
}
What value can be given to x such that the output is "Hello
World"?

I think you misrepresented the trick question.

With `x` an `int` it will never work.

However, if you `#define x` appropriatelly, you can get the desired
effect. E.g.:

#define x (!printf("Hello "))

will do the trick. Obviously, once you correct your code to something
that actually resembles C:

#include <stdio.h>

#define x (!printf("Hello, "))

int main(void)
{
if(x)
printf("Hello");
else
printf("World");

printf("\n");

return 0;
}

 

[Chris Dollin]

void main
{

`main` is a function that returns `int`, not a non-function
of type `void` and value `bother, there was a syntax error`.

int x;
if(x)
printf("Hello");
else
printf("World");
}
What value can be given to x such that the output is "Hello
World"?

There isn't one.

If you didn't mean /value/, but /initialiser/, then easy-peasy.

 

[Richard Heathfield]

Piyush Agarwal said:

void main
{
int x;
if(x)
printf("Hello");
else
printf("World");
}
What value can be given to x such that the output is "Hello
World"?

The output of the program is undefined for no fewer than three different
reasons. So it might well say "Hello World" as written. Or, of course, it
might not.

Until you understand what the three reasons are, I recommend that you spend
less time with puzzle questions and more time with a good C book.

 

[Kenneth Brody]

void main
{
int x;
if(x)
printf("Hello");
else
printf("World");
}
What value can be given to x such that the output is "Hello
World"?

Given that you're on Google, why not just search the c.l.c archives for
the thread on the almost exact same question from a few weeks ago?

Perhaps you should give us your professor's name, as I'm sure we'd all
like to know who gives out such homework assignments.

Of course, given your syntax error on "void main" (and numerous other
things), your version of the "problem" is unsolvable.

--
+-------------------------+--------------------+-----------------------------+
| Kenneth J. Brody | www.hvcomputer.com | |
| kenbrody/at\spamcop.net | www.fptech.com | #include <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------------+
Don't e-mail me at: <mailto:[email protected]>

 

[John Devereux]

`main` is a function that returns `int`, not a non-function
of type `void` and value `bother, there was a syntax error`.


There isn't one.

If you didn't mean /value/, but /initialiser/, then easy-peasy.

OK, I'll bite.... What initialiser?

 

[Suman]

Piyush Agarwal wrote:

[ snip code with UB ]

I think you misrepresented the trick question.

With `x` an `int` it will never work.

#include <stdio.h>

int main(void)
{
int x = 0;
if ( (printf("Hello, "), x) )
printf("Hello");
else
printf("World\n");
return 0;
}

 

[Vladimir Oka]

OK, I'll bite.... What initialiser?

You can do:

int x = !printf("Hello ");

[The "solution" I overlooked in my earlier post.]

 

[Vladimir Oka]

Piyush Agarwal wrote:

[ snip code with UB ]

I think you misrepresented the trick question.

With `x` an `int` it will never work.

#include <stdio.h>

int main(void)
{
int x = 0;
if ( (printf("Hello, "), x) )
printf("Hello");
else
printf("World\n");
return 0;
}

I don't think you were allowed to change the `if` statement. Have a
look at my other post as well.

 

[John Devereux]

OK, I'll bite.... What initialiser?

You can do:

int x = !printf("Hello ");

[The "solution" I overlooked in my earlier post.]

Aha!

 

[Suman]

Piyush Agarwal wrote:

[ snip code with UB ]

What value can be given to x such that the output is "Hello
World"?

I think you misrepresented the trick question.

With `x` an `int` it will never work.

#include <stdio.h>

int main(void)
{
int x = 0;
if ( (printf("Hello, "), x) )
printf("Hello");
else
printf("World\n");
return 0;
}

I don't think you were allowed to change the `if` statement. Have a
look at my other post as well.

Show me where this constraint was mentioned
Also your _other_ post came in a minute too late, I'd
already posted my reply before it came to being.

 

[Vladimir Oka]

Vladimir Oka wrote:
Piyush Agarwal wrote:

[ snip code with UB ]

What value can be given to x such that the output is "Hello
World"?

I think you misrepresented the trick question.

With `x` an `int` it will never work.

#include <stdio.h>

int main(void)
{
int x = 0;
if ( (printf("Hello, "), x) )
printf("Hello");
else
printf("World\n");
return 0;
}

I don't think you were allowed to change the `if` statement. Have a
look at my other post as well.

Show me where this constraint was mentioned
Also your _other_ post came in a minute too late, I'd
already posted my reply before it came to being.

Well, it wasn't mentioned in so many words. I thought it was implied.
Still, you could even do someting like:

if ( x = !printf("Hello ") )

or even better:

if ( x = (printf("Hello ") != 6) )

;-)

 

[Chris Dollin]

OK, I'll bite.... What initialiser?

You can do:

int x = !printf("Hello ");

[The "solution" I overlooked in my earlier post.]

S'not portable - there's no final newline after the World.

int x = (printf( "Hello, World\n" ), exit( 0 ), 17);

will do fine.

 

[Chris Dollin]

Vladimir Oka wrote:
Piyush Agarwal wrote:

[ snip code with UB ]

What value can be given to x such that the output is "Hello
World"?

I think you misrepresented the trick question.

With `x` an `int` it will never work.

#include <stdio.h>

int main(void)
{
int x = 0;
if ( (printf("Hello, "), x) )
printf("Hello");
else
printf("World\n");
return 0;
}

I don't think you were allowed to change the `if` statement. Have a
look at my other post as well.

Show me where this constraint was mentioned

Oh, in /that/ case:

int main() { printf( "Hello, World\n" ); }

will do.

 

[Vladimir Oka]

Piyush Agarwal wrote:

void main
{

`main` is a function that returns `int`, not a non-function
of type `void` and value `bother, there was a syntax error`.

int x;
if(x)
printf("Hello");
else
printf("World");
}
What value can be given to x such that the output is "Hello
World"?

There isn't one.

If you didn't mean /value/, but /initialiser/, then easy-peasy.

OK, I'll bite.... What initialiser?

You can do:

int x = !printf("Hello ");

[The "solution" I overlooked in my earlier post.]

S'not portable - there's no final newline after the World.

int x = (printf( "Hello, World\n" ), exit( 0 ), 17);

will do fine.

Yep. Using 42 instead of 17 would have been even better. ;-)

I was however building on the code I supplied in my original reply to
the OP (which did include the terminating '\n').

 

[Chris Dollin]

Yep. Using 42 instead of 17 would have been even better. ;-)

No, it wouldn't - I didn't wish to allude to tHGttG. Instead I alluded
to something else.

 

[Vladimir Oka]

No, it wouldn't - I didn't wish to allude to tHGttG. Instead I alluded
to something else.

You got me there. I dont get the allusion.

[17 *is*, more often than not, my staple "random" value, but I doubt
you know me that well. ;-)]

 

[Keith Thompson]

Piyush Agarwal said:


The output of the program is undefined for no fewer than three different
reasons. So it might well say "Hello World" as written. Or, of course, it
might not.

Until you understand what the three reasons are, I recommend that you spend
less time with puzzle questions and more time with a good C book.

I see four reasons (one of which is unlikely to cause mere undefined
behavior).

 

[Martin Ambuhl]

void main

^^^^ dead akready: main returns an int

{
int x;
if(x)

^^^ dead again: x is not initialized

printf("Hello");

^^^^^^ dead again; a variadic function with no declaration in
scope

else
printf("World");

For pre-C99 compilers (and with any decent coding standards even
with C99), dead again without a returned value.

}
What value can be given to x such that the output is "Hello
World"?

We answered this already, several times over. Please check the archives
before posting. Although it is not relevant to your question (but is
to your horrid code), check the FAQ before posting as well.

 

[Richard Heathfield]

Keith Thompson said:

I see four reasons (one of which is unlikely to cause mere undefined
behavior).

Believe it or not, the syntax error completely passed me by.