[C++ Question] For loop Multiple Initialization

[charlie.xia.fdu]

Hi C++ users,

for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

example from: http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.
Is there multiple initialization in C++? How can we use that?

Thanks!

Charlie

[Pawel Dziepak]

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ch*************@gmail.com wrote:

Hi C++ users,

for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

example from: http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.
Is there multiple initialization in C++? How can we use that?

That way is correct:

for (int i=0, j=10; i<5 && j<10; i++, j--) {}

Unless I'm wrong, there's no way to initialize variables of different
types in that part of for loop.

Pawel Dziepak

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[charlie.xia.fdu]

On Nov 3, 1:39*pm, Pawel Dziepak <[e-mail]:

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Hash: SHA1

[e-mail] wrote:

Hi C++ users,

for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

example from:http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.
Is there multiple initialization in C++? How can we use that?

That way is correct:

for (int i=0, j=10; i<5 && j<10; i++, j--) {}

Unless I'm wrong, there's no way to initialize variables of different
types in that part of for loop.

Pawel Dziepak

it works!
thanks

>
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[James Kanze]

On Nov 3, 10:29*pm, "[e-mail]" <[e-mail]>
wrote:

for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

example from:http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.

It's not valid in C++ either. Just another case of someone who
doesn't know the language trying to write about it.

Is there multiple initialization in C++?

Sort of. You can only write one declaration statement, but it
can define multiple variables, e.g.:

for ( int i = 0, j = 10 ; ... )

Generally speaking, i'ld avoid it, because it is confusing to
have multiple variables defined in the same declaration. But
there are probably exceptions; I know that some people like:

for ( Container::const_iterator
current = c.begin(), end = c.end() ;
current != end ;
++ current )

I'm not that fond of it, but if you raise it to the level of a
"standard idiom" in your code, I don't think I'd have any real
objections.

--
James Kanze (GABI Software) email:ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[James Kanze]

Pawel Dziepak wrote:

ch*************@gmail.com wrote:

for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

example from: http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.
Is there multiple initialization in C++? How can we use that?

That way is correct:

for (int i=0, j=10; i<5 && j<10; i++, j--) {}

Unless I'm wrong, there's no way to initialize variables of
different types in that part of for loop.

for ( int i = 0 , *p = &i ; ... )

:-).

Not that I'd like to maintain code which did such things.

--
James Kanze (GABI Software) email:ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[blargg]

Pawel Dziepak wrote:

ch*************@gmail.com wrote:

for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

example from: http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.
Is there multiple initialization in C++? How can we use that?

That way is correct:

for (int i=0, j=10; i<5 && j<10; i++, j--) {}

Unless I'm wrong, there's no way to initialize variables of different
types in that part of for loop.

I'll probably regret this, but I believe you can:

double d;
int* p;
for ( char c = (d = 1.234, p = new int, 'X'); ...

[Pete Becker]

On 2008-11-03 23:03:16 -0500, bl********@gishpuppy.com (blargg) said:

Pawel Dziepak wrote:

>ch*************@gmail.com wrote:

>>for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

example from: http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.
Is there multiple initialization in C++? How can we use that?

That way is correct:

for (int i=0, j=10; i<5 && j<10; i++, j--) {}

Unless I'm wrong, there's no way to initialize variables of different
types in that part of for loop.

I'll probably regret this, but I believe you can:

double d;
int* p;
for ( char c = (d = 1.234, p = new int, 'X'); ...

Or, less cryptically,

double d;
int *p;
char c;
for (c = 'X', d = 1.234, p = new int; ...

Now, technically, that's not initialization, but it may well be what
was actually meant.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[charlie.xia.fdu]

But actually I want these variables only in the scope of for loop.
Keep the initialization and increment in the for statement is the only
neat way I can think of.
Isn't it?
On Nov 4, 2:20*am, Pete Becker <[e-mail]:

On 2008-11-03 23:03:16 -0500, [e-mail] (blargg) said:

Pawel Dziepak wrote:

[e-mail] wrote:
for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

>example from:http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.
Is there multiple initialization in C++? How can we use that?

That way is correct:

for (int i=0, j=10; i<5 && j<10; i++, j--) {}

Unless I'm wrong, there's no way to initialize variables of different
types in that part of for loop.

I'll probably regret this, but I believe you can:

* * double d;
* * int* p;
* * for ( char c = (d = 1.234, p = new int, 'X'); ...

Or, less cryptically,

double d;
int *p;
char c;
for (c = 'X', d = 1.234, p = new int; ...

Now, technically, that's not initialization, but it may well be what
was actually meant.

--
* Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[Pete Becker]

On 2008-11-06 12:16:21 -0500, "ch*************@gmail.com"
<lx******@gmail.comsaid:

On Nov 4, 2:20Â*am, Pete Becker <[e-mail]:

>On 2008-11-03 23:03:16 -0500, [e-mail] (blargg) said:

>>Pawel Dziepak wrote:
[e-mail] wrote:
for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

>>>>example from:http://www.tech-faq.com/iterations.shtml
Is not valid in my eclipse cdt.
Is there multiple initialization in C++? How can we use that?

>>>That way is correct:

>>>for (int i=0, j=10; i<5 && j<10; i++, j--) {}

>>>Unless I'm wrong, there's no way to initialize variables of different
types in that part of for loop.

>>I'll probably regret this, but I believe you can:

>>Â* Â* double d;
Â* Â* int* p;
Â* Â* for ( char c = (d = 1.234, p = new int, 'X'); ...

Or, less cryptically,

double d;
int *p;
char c;
for (c = 'X', d = 1.234, p = new int; ...

Now, technically, that's not initialization, but it may well be what
was actually meant.

But actually I want these variables only in the scope of for loop.
Keep the initialization and increment in the for statement is the only
neat way I can think of.
Isn't it?

You can't have everything. In general, though, a for loop that requires
three loop control variables is almost certainly a mistake.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[blargg]

ch*************@gmail.com wrote:

On Nov 4, 2:20 am, Pete Becker <[e-mail]:

On 2008-11-03 23:03:16 -0500, [e-mail] (blargg) said:

Pawel Dziepak wrote:
>[e-mail] wrote:
>>for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

>>example from:http://www.tech-faq.com/iterations.shtml
>>Is not valid in my eclipse cdt.
>>Is there multiple initialization in C++? How can we use that?

>That way is correct:

>for (int i=0, j=10; i<5 && j<10; i++, j--) {}

>Unless I'm wrong, there's no way to initialize variables of different
>types in that part of for loop.

I'll probably regret this, but I believe you can:

double d;
int* p;
for ( char c = (d = 1.234, p = new int, 'X'); ...

Or, less cryptically,

double d;
int *p;
char c;
for (c = 'X', d = 1.234, p = new int; ...

Now, technically, that's not initialization, but it may well be what
was actually meant.

But actually I want these variables only in the scope of for loop.
Keep the initialization and increment in the for statement is the only
neat way I can think of.
Isn't it?

The for loop is for common loops that have a single variable that is
initialized, tested, and advanced. If it were made to handle every
possible loop, it would lose its usefulness. In fact, such a more general
loop construct already exists as a combination of a compound statement
({}) with a while or do-while loop in it. What do you gain by trying to
jam complicated things into a for loop anyway?

Also, please don't top-post, and don't quote signatures (see
<http://www.netmeister.org/news/learn2quote.html>).

[charlie]

On Nov 7, 1:08*am, [e-mail] (blargg) wrote:

[e-mail] wrote:

On Nov 4, 2:20 am, Pete Becker <[e-mail]:

On 2008-11-03 23:03:16 -0500, [e-mail] (blargg) said:
Pawel Dziepak wrote:
[e-mail] wrote:
>for(int i=0,int j=10 ; i<5&&j<10 ; i++ , j--) {}

>example from:http://www.tech-faq.com/iterations.shtml
>Is not valid in my eclipse cdt.
>Is there multiple initialization in C++? How can we use that?

That way is correct:

for (int i=0, j=10; i<5 && j<10; i++, j--) {}

Unless I'm wrong, there's no way to initialize variables of different
types in that part of for loop.

I'll probably regret this, but I believe you can:

* * double d;
* * int* p;
* * for ( char c = (d = 1.234, p = new int, 'X'); ...

Or, less cryptically,

double d;
int *p;
char c;
for (c = 'X', d = 1.234, p = new int; ...

Now, technically, that's not initialization, but it may well be what
was actually meant.

But actually I want these variables only in the scope of for loop.
Keep the initialization and increment in the for statement is the only
neat way I can think of.
Isn't it?

The for loop is for common loops that have a single variable that is
initialized, tested, and advanced. If it were made to handle every
possible loop, it would lose its usefulness. In fact, such a more general
loop construct already exists as a combination of a compound statement
({}) with a while or do-while loop in it. What do you gain by trying to
jam complicated things into a for loop anyway?

Also, please don't top-post, and don't quote signatures (see
<http://www.netmeister.org/news/learn2quote.html>).

Good to know. Thanks all.