Why can't I pass by value in this case??

[TaiwanNoWhere]

#include<iostre am>

using namespace std;

int main(void){

union Task{
int TaskNumber;
float Length;
};

// variables
static int TaskNumber= 0;
const int SIZE = 100;
int NumberOfTask = 0;
Task Schedule[SIZE];


cout<<"How many tasks are there?";
cin >>NumberOfTas k;

// ask for input
cout<<"Please enter the length of tasks (mins):"<<endl;
for(int i=0; i<NumberOfTask ; i++)
{
int Length = 0;

// Assign task number
TaskNumber++;
cout << TaskNumber << endl;
Schedule[i].TaskNumber= TaskNumber;
cout << Schedule[i].TaskNumber << endl;

// request for the length of each task
cout<<"Number "<< Schedule[i].TaskNumber <<" task takes :";
cin >>Length; // note: ensure length of time within 240
Schedule[i].Length= Length;
cout << "TaskNumber " << TaskNumber << endl;
cout << "Schedule[i].TaskNumber " << Schedule[i].TaskNumber << endl;

}

// display user's input
for(int i=0; i<NumberOfTask ; i++)
{
cout <<"Number "<< Schedule[i].TaskNumber <<" task takes "
<< Schedule[i].Length <<" minutes."<< endl;
}

// arrange in order of length of task

return 0;
}


//---------------------------------------------------//
How can I solve this?
Please help, thanks :)

[Kevin Goodsell]

Re: Why can't I pass by value in this case??

TaiwanNoWhere wrote:

<snip code>
[color=blue]
>
>
> //---------------------------------------------------//
> How can I solve this?
> Please help, thanks :)[/color]

Uh, what's the question?

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

[TaiwanNoWhere]

Re: Why can't I pass by value in this case??

The problem is Schedule.TaskNu mber will lose the value which I
assigned by ++TaskNumber

[WW]

Re: Why can't I pass by value in this case??

TaiwanNoWhere wrote:[color=blue]
> The problem is Schedule.TaskNu mber will lose the value which I
> assigned by ++TaskNumber[/color]

Loose? When, where?

--
WW aka Attila

[David B. Held]

Re: Why can't I pass by value in this case??

"TaiwanNoWh ere" <rudyliang@hotm ail.com> wrote in message
news:d8b9947c.0 310060645.21561 6a7@posting.goo gle.com...[color=blue]
> The problem is Schedule.TaskNu mber will lose the value
> which I assigned by ++TaskNumber[/color]

That's because union members *share* storage (but not
dues). When you assign to Schedule[i].Length, you are
*overwriting* the storage used by the other members of
the union, and thus their values are no longer valid. It
looks to me like you want Task to be a struct, not a union.
Also, a static var declared inside main() is kinda funny,
since I believe main() is not re-entrant in C++. Then
again, you wrote "main(void) ", so maybe it's supposed to
be a C program.

It really helps if you format your code nicely. Namely, use
proper indenting so loop structures and data structures
are obvious. Left-justified code is rarely read, hence
part of your difficulty in getting a useful response.

Dave



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[Jonathan Mcdougall]

Re: Why can't I pass by value in this case??

> #include<iostre am>[color=blue]
>
> using namespace std;[/color]

Are you sure you need that ?
[color=blue]
> int main(void){[/color]

(void) is considered bad style in C++

int main()
{
[color=blue]
> union Task{
> int TaskNumber;
> float Length;
> };[/color]

Yurk. Why do you use a union? BTW, this is the source
of your problem. A union shares the memory between its
members so you just cannot use them at the same time.
[color=blue]
> // variables
> static int TaskNumber= 0;[/color]

What's the static for ? It is illegal to call main()
multiple times.
[color=blue]
> const int SIZE = 100;
> int NumberOfTask = 0;
> Task Schedule[SIZE];
>
>
> cout<<"How many tasks are there?";
> cin >>NumberOfTas k;[/color]

What if the user enters 200 ? Did you consider
using std::vector ? Think : if I enter 3 tasks, there
is 97 elements wasted in 'Schedule'. If I enter 200,
there is a _big_ problem.

Look up std::vector in your book.
[color=blue]
> // ask for input
> cout<<"Please enter the length of tasks (mins):"<<endl;
> for(int i=0; i<NumberOfTask ; i++)[/color]

Prefer ++i when you don't need the return value.
[color=blue]
> {
> int Length = 0;
>
> // Assign task number
> TaskNumber++;
> cout << TaskNumber << endl;
> Schedule[i].TaskNumber= TaskNumber;[/color]

TaskNumber is used here, so Length is invalid.
[color=blue]
> cout << Schedule[i].TaskNumber << endl;
>
> // request for the length of each task
> cout<<"Number "<< Schedule[i].TaskNumber <<" task takes :";
> cin >>Length; // note: ensure length of time within 240
> Schedule[i].Length= Length;[/color]

Length is used here so TaskNumber is invalid.
[color=blue]
> cout << "TaskNumber " << TaskNumber << endl;
> cout << "Schedule[i].TaskNumber " << Schedule[i].TaskNumber << endl;
>
> }
>
> // display user's input
> for(int i=0; i<NumberOfTask ; i++)
> {
> cout <<"Number "<< Schedule[i].TaskNumber <<" task takes "
> << Schedule[i].Length <<" minutes."<< endl;[/color]

Length was used the last, so TaskNumber prints garbage.
[color=blue]
> }[/color]
[color=blue]
> How can I solve this?[/color]

Don't use a union, use a struct or a class.


Jonathan

[David B. Held]

Re: Why can't I pass by value in this case??

"Jonathan Mcdougall" <jonathanmcdoug all@DELyahoo.ca > wrote in message
news:5pjgb.5092 0$282.698849@we ber.videotron.n et...[color=blue][color=green]
> > #include<iostre am>
> >
> > using namespace std;[/color]
>
> Are you sure you need that ?[/color]

Does it matter if he needs it?
[color=blue][color=green]
> > int main(void){[/color]
>
> (void) is considered bad style in C++
>
> int main()
> {[/color]

The only thing that suprises me here is that you didn't go all
the way and say that K&R style braces are also bad style in
C++.
[color=blue]
> [...]
> What's the static for ? It is illegal to call main() multiple
> times.
> [...][/color]

It's illegal for the user to call main() one time.

Dave



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[David B. Held]

Re: Why can't I pass by value in this case??

"Jonathan Mcdougall" <jonathanmcdoug all@DELyahoo.ca > wrote in message
news:5pjgb.5092 0$282.698849@we ber.videotron.n et...[color=blue][color=green]
> > #include<iostre am>
> >
> > using namespace std;[/color]
>
> Are you sure you need that ?[/color]

Does it matter if he needs it?
[color=blue][color=green]
> > int main(void){[/color]
>
> (void) is considered bad style in C++
>
> int main()
> {[/color]

The only thing that suprises me here is that you didn't go all
the way and say that K&R style braces are also bad style in
C++.
[color=blue]
> [...]
> What's the static for ? It is illegal to call main() multiple
> times.
> [...][/color]

It's illegal for the user to call main() one time.

Dave



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.521 / Virus Database: 319 - Release Date: 9/23/2003

[Jonathan Mcdougall]

Re: Why can't I pass by value in this case??

> > > #include<iostre am>[color=blue][color=green][color=darkred]
> > >
> > > using namespace std;[/color]
> >
> > Are you sure you need that ?[/color]
>
> Does it matter if he needs it?[/color]

Of course. What is your point?
[color=blue][color=green][color=darkred]
> > > int main(void){[/color]
> >
> > (void) is considered bad style in C++
> >
> > int main()
> > {[/color]
>
> The only thing that suprises me here is that you didn't go all
> the way and say that K&R style braces are also bad style in
> C++.[/color]

Braces are a matter of taste. Putting (void) for an empty
parameter list is bad style in C++, except for C compatibility.
[color=blue][color=green]
> > [...]
> > What's the static for ? It is illegal to call main() multiple
> > times.
> > [...][/color]
>
> It's illegal for the user to call main() one time.[/color]

Yes, but this is not what I said. It is illegal to call main()
multiple time, since main() is called once by the operating
system.


Jonathan

[Jack Klein]

Re: Why can't I pass by value in this case??

On Mon, 6 Oct 2003 15:04:59 -0400, "Jonathan Mcdougall"
<jonathanmcdoug all@DELyahoo.ca > wrote in comp.lang.c++:
[color=blue][color=green]
> > #include<iostre am>
> >
> > using namespace std;[/color]
>
> Are you sure you need that ?
>[color=green]
> > int main(void){[/color]
>
> (void) is considered bad style in C++[/color]

By whom? "style" is a matter of opinion. Can you cite a link to the
C++ standard where this is either deprecated or marked obsolescent?

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
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alt.comp.lang.l earn.c-c++ ftp://snurse-l.org/pub/acllc-c++/faq

[Jonathan Mcdougall]

Re: Why can't I pass by value in this case??

> > > #include<iostre am>[color=blue][color=green][color=darkred]
> > >
> > > using namespace std;[/color]
> >
> > Are you sure you need that ?
> >[color=darkred]
> > > int main(void){[/color]
> >
> > (void) is considered bad style in C++[/color]
>
> By whom?[/color]

The C++ community in general.
[color=blue]
>"style" is a matter of opinion.[/color]

I would rather say that "style" is a mix of taste and
language-specific features and constraints.
[color=blue]
> Can you cite a link to the
> C++ standard where this is either deprecated or marked obsolescent?[/color]

No, that is why I asked if it was deprecated or not in another post
("void and this" by Vladimir Grul).


Jonathan

[TaiwanNoWhere]

Re: Why can't I pass by value in this case??

Thanks everyone's response.
After I copy and paste the codes here, the format is lost.:(
Therefore, sorry for my codes.