using OUT in a method

[Pascal]

hello everybody !
I get this error 3 times : "The output parameter must be assigned before
the control leaves the current method" (dor dMin and dMax)
this one 1 time : Use of the parameter 'out' is not assigned 'dMax'

This is my first steps in C#: i can't manage(understa nd) this error.

I would like to test to variables which can be change on form1 by 2 numeric
updown controls before sending them to a UserControl which make some
calculation with these 2 numbers like this :

if (_genData.Numbe rMin < _genData.Number Max)
{

S = (int)(_rand.Nex t((int)_genData .NumberMin,
(int)_genData.N umberMax + 1) / 3) * 3;
}

else
{
//Choisir le nombre cible (_iS) compris dans la fourchette
et le rendre multiple de trois.
// Set the target number (_iS) in the range and make
multiple of three.
So if user modify the value and nudNumMin .Value becomes nudNumMax
..Value the calculation could send an error in calculating the value S.
That's why i have to test and correct the values before sending them to the
UserControl.

the code in form1 is :
#region min max check
string message = "Attention ! Le nombre maximal doit être au
nombre minimal. L'erreur sera corrigée";
string caption = "Erreur dans le choix de la taille des nombres.";
MessageBoxButto ns buttons = MessageBoxButto ns.OK;
DialogResult result;

// this method checks the values and shows an error message if
// they are not as expected and corrects them to a valid state

public bool CheckMinMaxValu es(out int dMin, out int dMax)
{

if ( nudNumMin .Value nudNumMax .Value )
{
result = MessageBox.Show (message, caption, buttons);
dMin = dMax - 1;
return false;
}
return true;
}
#endregion //min max check

and then :

private void nudNumMax_Value Changed( object sender, EventArgs e )
{
int dMin = (int)nudNumMin. Value;
int dMax = (int)nudNumMax. Value;
if (!CheckMinMaxVa lues(out dMin, out dMax))
{
//... do what ever is needed when the check fails
nudNumMin.Value = dMin;
nudNumMax.Value = dMax;
nudNumMax.Value = nudNumMin.Value + 1;
_currParam.Gene rationData.Numb erMax = (int) nudNumMin.Value
+ 1; // for example

}
_currParam.Gene rationData.Numb erMax = (int)nudNumMax. Value;
ValueChanged( true );
}

I hope you understand me....
and can help me !
pascal
--
http://www.scalpa.info

[Jesse McGrew]

On Apr 13, 12:58 am, "Pascal" <scalpaSansS... @scalpa.infowro te:

hello everybody !
I get this error 3 times : "The output parameter must be assigned before
the control leaves the current method" (dor dMin and dMax)
this one 1 time : Use of the parameter 'out' is not assigned 'dMax'

This is my first steps in C#: i can't manage(understa nd) this error.

The code you posted doesn't modify dMax, so dMax doesn't need to be an
out parameter. Remove the "out" keyword for dMax and it should work.

Jesse

[BlackWasp]

Have a look at http://www.blackwasp.co.uk/CSharpMethodParameters.aspx for
details on output parameters.

--

BlackWasp
www.blackwasp.co.uk
"Pascal" <sc************ @scalpa.infowro te in message
news:66******** *************** ***********@mic rosoft.com...

hello everybody !
I get this error 3 times : "The output parameter must be assigned before
the control leaves the current method" (dor dMin and dMax)
this one 1 time : Use of the parameter 'out' is not assigned 'dMax'

This is my first steps in C#: i can't manage(understa nd) this error.

I would like to test to variables which can be change on form1 by 2
numeric updown controls before sending them to a UserControl which make
some calculation with these 2 numbers like this :

if (_genData.Numbe rMin < _genData.Number Max)
{

S = (int)(_rand.Nex t((int)_genData .NumberMin,
(int)_genData.N umberMax + 1) / 3) * 3;
}

else
{
//Choisir le nombre cible (_iS) compris dans la fourchette
et le rendre multiple de trois.
// Set the target number (_iS) in the range and make
multiple of three.
So if user modify the value and nudNumMin .Value becomes nudNumMax
.Value the calculation could send an error in calculating the value S.
That's why i have to test and correct the values before sending them to
the UserControl.

the code in form1 is :
#region min max check
string message = "Attention ! Le nombre maximal doit être au
nombre minimal. L'erreur sera corrigée";
string caption = "Erreur dans le choix de la taille des nombres.";
MessageBoxButto ns buttons = MessageBoxButto ns.OK;
DialogResult result;

// this method checks the values and shows an error message if
// they are not as expected and corrects them to a valid state

public bool CheckMinMaxValu es(out int dMin, out int dMax)
{

if ( nudNumMin .Value nudNumMax .Value )
{
result = MessageBox.Show (message, caption, buttons);
dMin = dMax - 1;
return false;
}
return true;
}
#endregion //min max check

and then :

private void nudNumMax_Value Changed( object sender, EventArgs e )
{
int dMin = (int)nudNumMin. Value;
int dMax = (int)nudNumMax. Value;
if (!CheckMinMaxVa lues(out dMin, out dMax))
{
//... do what ever is needed when the check fails
nudNumMin.Value = dMin;
nudNumMax.Value = dMax;
nudNumMax.Value = nudNumMin.Value + 1;
_currParam.Gene rationData.Numb erMax = (int) nudNumMin.Value
+ 1; // for example

}
_currParam.Gene rationData.Numb erMax = (int)nudNumMax. Value;
ValueChanged( true );
}

I hope you understand me....
and can help me !
pascal
--
http://www.scalpa.info

[Duy Lam]

Pascal wrote:

hello everybody !
I get this error 3 times : "The output parameter must be assigned
before the control leaves the current method" (dor dMin and dMax)
this one 1 time : Use of the parameter 'out' is not assigned 'dMax'

This is my first steps in C#: i can't manage(understa nd) this error.

I would like to test to variables which can be change on form1 by 2
numeric updown controls before sending them to a UserControl which make
some calculation with these 2 numbers like this :

if (_genData.Numbe rMin < _genData.Number Max)
{

S = (int)(_rand.Nex t((int)_genData .NumberMin,
(int)_genData.N umberMax + 1) / 3) * 3;
}

else
{
//Choisir le nombre cible (_iS) compris dans la
fourchette et le rendre multiple de trois.
// Set the target number (_iS) in the range and make
multiple of three.
So if user modify the value and nudNumMin .Value becomes nudNumMax
.Value the calculation could send an error in calculating the value S.
That's why i have to test and correct the values before sending them to
the UserControl.

the code in form1 is :
#region min max check
string message = "Attention ! Le nombre maximal doit être au
nombre minimal. L'erreur sera corrigée";
string caption = "Erreur dans le choix de la taille des nombres.";
MessageBoxButto ns buttons = MessageBoxButto ns.OK;
DialogResult result;

// this method checks the values and shows an error message if
// they are not as expected and corrects them to a valid state

public bool CheckMinMaxValu es(out int dMin, out int dMax)
{

if ( nudNumMin .Value nudNumMax .Value )
{
result = MessageBox.Show (message, caption, buttons);
dMin = dMax - 1;
return false;
}
return true;
}
#endregion //min max check

and then :

private void nudNumMax_Value Changed( object sender, EventArgs e )
{
int dMin = (int)nudNumMin. Value;
int dMax = (int)nudNumMax. Value;
if (!CheckMinMaxVa lues(out dMin, out dMax))
{
//... do what ever is needed when the check fails
nudNumMin.Value = dMin;
nudNumMax.Value = dMax;
nudNumMax.Value = nudNumMin.Value + 1;
_currParam.Gene rationData.Numb erMax = (int)
nudNumMin.Value + 1; // for example

}
_currParam.Gene rationData.Numb erMax = (int)nudNumMax. Value;
ValueChanged( true );
}

I hope you understand me....
and can help me !
pascal

If you use the "out" keyword for the parameters, you must assign the
value to it before go out of method. The "out" keyword requires that.
In your method CheckMinMaxValu es(), the value of two "out" parameters
will not be set if the "if" statement is false, so the compiler didn't work.

--
Thanks,
Duy Lam Phuong

[Jon Skeet [C# MVP]]

On Apr 13, 1:12 am, "BlackWasp" <nospam@pleasew rote:

Have a look athttp://www.blackwasp.c o.uk/CSharpMethodPar ameters.aspxfor
details on output parameters.

That article and its predecessor propagate the "objects are passed by
reference" myth which confuses people who know what pass-by-reference
semantics really mean.

See http://pobox.com/~skeet/csharp/parameters.html for a more accurate
description.

Jon

[Alun Harford]

BlackWasp wrote:

Have a look at http://www.blackwasp.co.uk/CSharpMethodParameters.aspx
for details on output parameters.

Eugh.

While it's always good to have more reference material out there for
people to learn from, I think you need to read the C# specification and
then go back and correct some of the bugs.

In particular:

"So far in the C# Fundamentals tutorial, we have created methods that
accept parameters and return a single value. These parameters are known
as value parameters. This is because when used with value types such as
the numeric types and structures, a copy of the value of the parameter
is passed to the method."

This seems to imply that reference types are not passed by reference.
This is incorrect. They are passed by value (that value is a reference).

"An output parameter is declared using the out keyword before the
parameter type and name. To return a value using the parameter, the
variable is simply assigned a value."

An output parameter doesn't ever 'return' a value. It just represents
the same storage location as the variable used as the argument in the
method invocation.

"When an object based upon any class is passed to a method as a
parameter, the object is passed by reference"

This is wrong.
Reference types passed into value parameters are not passed by reference
- they're passed by value.

"It is possible to create the same behaviour for value types by
declaring a parameter to be a reference parameter"

The behaviour is very different, and you can pass reference types by
reference in the same way.

Alun Harford

[Pascal]

Thanks for your help, it took me a while to understand every thing ....
Thanks for the link too.

[BlackWasp]

I hear what you are saying but remember that this is a _fundamentals_
tutorial for beginners. Some would say that the semantics are very
important. In my experience they may be but beginners can get too wrapped
up in them and end up confused rather than developing.

eg. Yes, out parameters don't return a value but to beginners, that is the
effect.

It's swings and roundabouts but I am going to tidy up a few sentences.

Cheers!

--

BlackWasp
www.blackwasp.co.uk
"Alun Harford" <de*****@alunha rford.co.ukwrot e in message
news:%2******** ********@TK2MSF TNGP03.phx.gbl. ..

BlackWasp wrote:

>Have a look at http://www.blackwasp.co.uk/CSharpMethodParameters.aspx for
details on output parameters.

Eugh.

While it's always good to have more reference material out there for
people to learn from, I think you need to read the C# specification and
then go back and correct some of the bugs.

In particular:

"So far in the C# Fundamentals tutorial, we have created methods that
accept parameters and return a single value. These parameters are known
as value parameters. This is because when used with value types such as
the numeric types and structures, a copy of the value of the parameter is
passed to the method."

This seems to imply that reference types are not passed by reference. This
is incorrect. They are passed by value (that value is a reference).

"An output parameter is declared using the out keyword before the
parameter type and name. To return a value using the parameter, the
variable is simply assigned a value."

An output parameter doesn't ever 'return' a value. It just represents the
same storage location as the variable used as the argument in the method
invocation.

"When an object based upon any class is passed to a method as a parameter,
the object is passed by reference"

This is wrong.
Reference types passed into value parameters are not passed by reference -
they're passed by value.

"It is possible to create the same behaviour for value types by declaring
a parameter to be a reference parameter"

The behaviour is very different, and you can pass reference types by
reference in the same way.

Alun Harford

[Jon Skeet [C# MVP]]

On Apr 18, 10:11 am, "BlackWasp" <nospam@pleasew rote:

I hear what you are saying but remember that this is a _fundamentals_
tutorial for beginners.

I would say that correctly differentiating between passing a reference
by value and passing a parameter by reference is quite fundamental. It
affects the whole mental model of how objects are stored.

Some would say that the semantics are very
important. In my experience they may be but beginners can get too wrapped
up in them and end up confused rather than developing.

I would personally rather beginners took a little bit longer to learn
the fundamentals, than came away with a broken mental model which is
much harder to undo later on.

Jon

[Jon Skeet [C# MVP]]

On Apr 18, 1:41 pm, "BlackWasp" <nospam@pleasew rote:

you may be right. There are always two approaches to a problem. As I said
to Alun, I am making some minor changes. I am on the side of the fence that
believes that overall concepts are more appropriate for beginners than
finite details. I can understand that some people disagree with this
approach while some support it.

There's a difference between omitting fine details and stating
outright falsehoods, however. I'm fine with the idea of leaving a sign
saying "here be dragons" around particularly difficult bits, and
perhaps coming back to them later - but anything which encourages a
beginner to believe something which is actually untrue is a bad thing,
IMO - simply because "unlearning " is difficult.

I'm actually of the belief that the truth about the nature of
references and objects is easier to grasp than we think - it's just
*very* hard to write about clearly. The concept itself isn't that
hard, but explaining it is difficult. Personally I like the analogy of
a piece of paper for value types (to create a copy, you photocopy the
piece of paper) vs a web page for reference types (to tell a friend
about the page, you just give him a copy of the URL, rather than the
page itself).

The bonus of this is that once this fundamental concept has been
grasped, all kinds of things become *much* easier to explain -
assignment, parameter passing, garbage collection, memory allocation
etc.

Jon