variable declaration in if statement

[Denis Petronenko]

i can write something like this

int foo()
{
return 100;
}

if( int x=foo() ) {
....
}else{
....
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.

[David Harmon]

On 5 Aug 2006 12:09:44 -0700 in comp.lang.c++, "Denis Petronenko"
<pe********@gmail.comwrote,

>if( int x=foo() ) {
...
}else{
...
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.

Write it like:

int x = foo();
if( x < 50 ) {
....

With no looping, there's nothing about "If" to keep you from
splitting it into two more understandable statements like that.

[Jens Marder]

"David Harmon" <so****@netcom.comschrieb im Newsbeitrag
news:45****************@news.west.earthlink.net...

On 5 Aug 2006 12:09:44 -0700 in comp.lang.c++, "Denis Petronenko"
<pe********@gmail.comwrote,

>>if( int x=foo() ) {
...
}else{
...
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.

Write it like:

int x = foo();
if( x < 50 ) {
...

With no looping, there's nothing about "If" to keep you from
splitting it into two more understandable statements like that.

Why not use parantheses?

if( (int x=foo()) 50 ) {
....
}else{
....
}

[Denis Petronenko]

David Harmon wrote:

On 5 Aug 2006 12:09:44 -0700 in comp.lang.c++, "Denis Petronenko"
<pe********@gmail.comwrote,

if( int x=foo() ) {
...
}else{
...
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.

Write it like:

int x = foo();
if( x < 50 ) {
...

With no looping, there's nothing about "If" to keep you from
splitting it into two more understandable statements like that.

i don't want to use x variable after if statement and want to reduce
scope of x variable to if statement only.

[Denis Petronenko]

Jens Marder wrote:

"David Harmon" <so****@netcom.comschrieb im Newsbeitrag
news:45****************@news.west.earthlink.net...

On 5 Aug 2006 12:09:44 -0700 in comp.lang.c++, "Denis Petronenko"
<pe********@gmail.comwrote,

>if( int x=foo() ) {
...
}else{
...
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.

Write it like:

int x = foo();
if( x < 50 ) {
...

With no looping, there's nothing about "If" to keep you from
splitting it into two more understandable statements like that.

Why not use parantheses?

if( (int x=foo()) 50 ) {
...
}else{
...
}

because it doesn't compile. at least using this
g++ (GCC) 4.0.4 20060507 (prerelease) (Debian 4.0.3-3)

[Matt]

Jens Marder wrote:

"David Harmon" <so****@netcom.comschrieb im Newsbeitrag
news:45****************@news.west.earthlink.net...

>>On 5 Aug 2006 12:09:44 -0700 in comp.lang.c++, "Denis Petronenko"
<pe********@gmail.comwrote,

>>>if( int x=foo() ) {
...
}else{
...
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.

Write it like:

int x = foo();
if( x < 50 ) {
...

With no looping, there's nothing about "If" to keep you from
splitting it into two more understandable statements like that.

Why not use parantheses?

if( (int x=foo()) 50 ) {
...
}else{
...
}

That doesn't compile for me with g++. It seems that the 'int' has to
come before the second '('. However

#include <iostream>
using namespace std;

int foo() { return 100; }

int main(int argc, char *argv[]){
if (int x=foo() 50) {
cout << "condition true" << endl;
cout << "x == " << x << endl;
} else {
cout << "condition false" << endl;
cout << "x == " << x << endl;
}
}

does compile and seems to work as desired.

(int x= foo() 50) and (int x= (foo() 50)) seem to be equivalent in
this context.

(int x=foo() && (x>50)) seems to be legal but doesn't have the desired
meaning. '&&' has higher precedence than '=', so that the assignment
expression computes x in terms of its uninitialized self so that the
result is indeterminate.

[Alf P. Steinbach]

* Jens Marder:

>
Why not use parantheses?

if( (int x=foo()) 50 ) {
...
}else{
...
}

Because it doesn't conform to the 'if' statement syntax; it's the same
as you cannot put parentheses around a declaration elsewhere.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Matt]

Matt wrote:

Jens Marder wrote:

>"David Harmon" <so****@netcom.comschrieb im Newsbeitrag
news:45****************@news.west.earthlink.net.. .

>>On 5 Aug 2006 12:09:44 -0700 in comp.lang.c++, "Denis Petronenko"
<pe********@gmail.comwrote,

if( int x=foo() ) {
...
}else{
...
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.
Write it like:

int x = foo();
if( x < 50 ) {
...

With no looping, there's nothing about "If" to keep you from
splitting it into two more understandable statements like that.

Why not use parantheses?

if( (int x=foo()) 50 ) {
...
}else{
...
}

That doesn't compile for me with g++. It seems that the 'int' has to
come before the second '('. However

#include <iostream>
using namespace std;

int foo() { return 100; }

int main(int argc, char *argv[]){
if (int x=foo() 50) {
cout << "condition true" << endl;
cout << "x == " << x << endl;
} else {
cout << "condition false" << endl;
cout << "x == " << x << endl;
}
}

does compile and seems to work as desired.

whoops. x is left with the value of the '>' expression, namely 0 or 1,
so that this doesn't do what the OP wanted.

[Ian Collins]

Denis Petronenko wrote:

David Harmon wrote:

>>On 5 Aug 2006 12:09:44 -0700 in comp.lang.c++, "Denis Petronenko"
<pe********@gmail.comwrote,

>>>if( int x=foo() ) {
...
}else{
...
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.

Write it like:

int x = foo();
if( x < 50 ) {
...

With no looping, there's nothing about "If" to keep you from
splitting it into two more understandable statements like that.

i don't want to use x variable after if statement and want to reduce
scope of x variable to if statement only.

{
int x = foo();
if( x < 50 ) {
...
}
}
--
Ian Collins.

[Mark P]

Denis Petronenko wrote:

David Harmon wrote:

>On 5 Aug 2006 12:09:44 -0700 in comp.lang.c++, "Denis Petronenko"
<pe********@gmail.comwrote,

>>if( int x=foo() ) {
...
}else{
...
}

but, for example, how can i check that x>50 in the "if" statement? So,
the if will be true only if x>50.

Write it like:

int x = foo();
if( x < 50 ) {
...

With no looping, there's nothing about "If" to keep you from
splitting it into two more understandable statements like that.

i don't want to use x variable after if statement and want to reduce
scope of x variable to if statement only.

Then put braces around both the variable declaration and the if statement.

{
int x = foo();
if ( x < 50 ) { ... }
}