chnage the Array Element

[sh]

Hi All..

i am Writing a C# code ..but i had face a small problem ,
i hope that you can solve it Please.

I had creat the following class

class Q
{
int A;
Int B
}

then in the main i creat an array of the above class

Q[] Array_Q = new Q[55]();

then i tried to fill the elemnets with a values

int i,j;
for (i=0 ; i<=10 ; i++)
{
for (j=i;j<=10;j++)
Array_Q[i].A = i; //<== here is the error
Array_Q[i].B = j;
}
if I run the program it give me an Exchption handelling
Error ..!!
so what is the Problem do you think..
thank you All

[Jon Skeet]

sh <hs***@yahoo.com> wrote:

then in the main i creat an array of the above class

Q[] Array_Q = new Q[55]();
That creates an array of references, all of which are null to start
with. It doesn't create a single instance of Q. You need to change the
element to refer to a valid instance before doing anything else.
then i tried to fill the elemnets with a values

int i,j;
for (i=0 ; i<=10 ; i++)
{
for (j=i;j<=10;j++)
Put in: Array_Q[i] = new Q(); and it will work
Array_Q[i].A = i; //<== here is the error
Array_Q[i].B = j;
}

<snip>

It's very important to know the difference between reference types and
value types - if Q had been a value type, it would have worked. See
http://www.pobox.com/~skeet/csharp/parameters.html and
http://www.pobox.com/~skeet/csharp/memory.html

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet/
If replying to the group, please do not mail me too

[sh]

Ok .. thank you Mr.Jon Skeet
I will try it ... and I will see

Thank you agin

-----Original Message-----
sh <hs***@yahoo.com> wrote:

then in the main i creat an array of the above class

Q[] Array_Q = new Q[55]();
That creates an array of references, all of which are

null to startwith. It doesn't create a single instance of Q. You need to change theelement to refer to a valid instance before doing anything else.

then i tried to fill the elemnets with a values

int i,j;
for (i=0 ; i<=10 ; i++)
{
for (j=i;j<=10;j++)
Put in: Array_Q[i] = new Q(); and it will work

Array_Q[i].A = i; //<== here is the error
Array_Q[i].B = j;
}

<snip>

It's very important to know the difference between

reference types andvalue types - if Q had been a value type, it would have worked. Seehttp://www.pobox.com/~skeet/csharp/parameters.html and
http://www.pobox.com/~skeet/csharp/memory.html

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet/
If replying to the group, please do not mail me too
.

[David Lau]

Thanks, it is very useful for the beginner like me
"sh" <hs***@yahoo.com> wrote in message
news:03****************************@phx.gbl...

Ok .. thank you Mr.Jon Skeet
I will try it ... and I will see

Thank you agin

-----Original Message-----
sh <hs***@yahoo.com> wrote:

then in the main i creat an array of the above class

Q[] Array_Q = new Q[55]();

That creates an array of references, all of which are

null to start

with. It doesn't create a single instance of Q. You need

to change the

element to refer to a valid instance before doing

anything else.

then i tried to fill the elemnets with a values

int i,j;
for (i=0 ; i<=10 ; i++)
{
for (j=i;j<=10;j++)

Put in: Array_Q[i] = new Q(); and it will work

Array_Q[i].A = i; //<== here is the error
Array_Q[i].B = j;
}

<snip>

It's very important to know the difference between

reference types and

value types - if Q had been a value type, it would have

worked. See

http://www.pobox.com/~skeet/csharp/parameters.html and
http://www.pobox.com/~skeet/csharp/memory.html

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet/
If replying to the group, please do not mail me too
.