Jagged and Multi-Dimensional Array Declaration Subtleties

Hi everyone,

I'm new to C# and I was hoping I could get some clarification on the
syntax for jagged and multidimensional arrays.

Here is my question:

The following syntax is correct for declaring a multi-dimensional
array:

int[,] v = {{ 3, 6, 4 },
{ 2, 8, 1 }};

If I declare a similar jagged array, however, I have to do this
instead:

int[][] w = {new int[] { 3, 6, 4 },
new int[] { 2, 8, 1 }};

Specifically, the "new int[]" declarations are absolutely necessary to
avoid a compiler error. If you remove the "new int[]" from the
declaration you get this compiler error:

"Array initializers can only be used in a variable or
field initializer. Try using a new expression instead."

I know that v is a multi-dimensional array and w is an "array of int
array". So I understand the difference in semantics. But I can't
articulate *why* there is a difference in the syntax.

Thanks very much.
--
Alan

re: Jagged and Multi-Dimensional Array Declaration Subtleties

Alan Foxmore wrote:[color=blue]
> Hi everyone,
>
> I'm new to C# and I was hoping I could get some clarification on the
> syntax for jagged and multidimensional arrays.
>
> Here is my question:
>
> The following syntax is correct for declaring a multi-dimensional
> array:
>
> int[,] v = {{ 3, 6, 4 },
> { 2, 8, 1 }};
>
> If I declare a similar jagged array, however, I have to do this
> instead:
>
> int[][] w = {new int[] { 3, 6, 4 },
> new int[] { 2, 8, 1 }};
>
> Specifically, the "new int[]" declarations are absolutely necessary to
> avoid a compiler error. If you remove the "new int[]" from the
> declaration you get this compiler error:
>
> "Array initializers can only be used in a variable or
> field initializer. Try using a new expression instead."
>
> I know that v is a multi-dimensional array and w is an "array of int
> array". So I understand the difference in semantics. But I can't
> articulate *why* there is a difference in the syntax.
>
> Thanks very much.
> --
> Alan
>
>[/color]

I think you have a pretty clear understanding of the difference, that's
just how people in MS define the syntax.

You can look

int[][] w = {new int[] { 3, 6, 4 },
new int[] { 2, 8, 1 }};

this way:
int[][] w=new int[2][];
w[0]=new int[] { 3, 6, 4 }
w[1]=new int[] { 2, 8, 1 }

Then , you should know the new is required here.

Programming Language grammar is kind of similar with normal grammar, it
largely depends on how people define them.

Jianwei

re: Jagged and Multi-Dimensional Array Declaration Subtleties

"John Sun" <jsunnewsgroup@gmail.com> wrote in message
news:%23vsb5YeKGHA.3272@tk2msftngp13.phx.gbl...[color=blue]
> Alan Foxmore wrote:[color=green]
>> Hi everyone,
>>
>> I'm new to C# and I was hoping I could get some clarification on the
>> syntax for jagged and multidimensional arrays.
>>
>> Here is my question:
>>
>> The following syntax is correct for declaring a multi-dimensional
>> array:
>>
>> int[,] v = {{ 3, 6, 4 },
>> { 2, 8, 1 }};
>>
>> If I declare a similar jagged array, however, I have to do this
>> instead:
>>
>> int[][] w = {new int[] { 3, 6, 4 },
>> new int[] { 2, 8, 1 }};
>>
>> Specifically, the "new int[]" declarations are absolutely necessary
>> to avoid a compiler error. If you remove the "new int[]" from the
>> declaration you get this compiler error:
>>
>> "Array initializers can only be used in a variable or
>> field initializer. Try using a new expression instead."
>>
>> I know that v is a multi-dimensional array and w is an "array of int
>> array". So I understand the difference in semantics. But I can't
>> articulate *why* there is a difference in the syntax.
>>
>>
>>[/color]
>
> I think you have a pretty clear understanding of the difference,
> that's just how people in MS define the syntax.
>
> You can look
>
> int[][] w = {new int[] { 3, 6, 4 },
> new int[] { 2, 8, 1 }};
>
> this way:
> int[][] w=new int[2][];
> w[0]=new int[] { 3, 6, 4 }
> w[1]=new int[] { 2, 8, 1 }
>
> Then , you should know the new is required here.
>
> Programming Language grammar is kind of similar with normal grammar,
> it largely depends on how people define them.[/color]




Well, Thanks for the response but I was hoping for a more rigorous,
formal explanation. In your first example you're using an initializer
whereas in the second you're using assignment.

I may be wrong but I feel the real explanation is more precise than,
"...just how people in MS define the syntax".
--
Alan

re: Jagged and Multi-Dimensional Array Declaration Subtleties

Alan Foxmore wrote:[color=blue]
> "John Sun" <jsunnewsgroup@gmail.com> wrote in message
> news:%23vsb5YeKGHA.3272@tk2msftngp13.phx.gbl...[color=green]
>> Alan Foxmore wrote:[color=darkred]
>>> Hi everyone,
>>>
>>> I'm new to C# and I was hoping I could get some clarification on the
>>> syntax for jagged and multidimensional arrays.
>>>
>>> Here is my question:
>>>
>>> The following syntax is correct for declaring a multi-dimensional
>>> array:
>>>
>>> int[,] v = {{ 3, 6, 4 },
>>> { 2, 8, 1 }};
>>>
>>> If I declare a similar jagged array, however, I have to do this
>>> instead:
>>>
>>> int[][] w = {new int[] { 3, 6, 4 },
>>> new int[] { 2, 8, 1 }};
>>>
>>> Specifically, the "new int[]" declarations are absolutely necessary
>>> to avoid a compiler error. If you remove the "new int[]" from the
>>> declaration you get this compiler error:
>>>
>>> "Array initializers can only be used in a variable or
>>> field initializer. Try using a new expression instead."
>>>
>>> I know that v is a multi-dimensional array and w is an "array of int
>>> array". So I understand the difference in semantics. But I can't
>>> articulate *why* there is a difference in the syntax.
>>>
>>>
>>>[/color]
>> I think you have a pretty clear understanding of the difference,
>> that's just how people in MS define the syntax.
>>
>> You can look
>>
>> int[][] w = {new int[] { 3, 6, 4 },
>> new int[] { 2, 8, 1 }};
>>
>> this way:
>> int[][] w=new int[2][];
>> w[0]=new int[] { 3, 6, 4 }
>> w[1]=new int[] { 2, 8, 1 }
>>
>> Then , you should know the new is required here.
>>
>> Programming Language grammar is kind of similar with normal grammar,
>> it largely depends on how people define them.[/color]
>
>
>
>
> Well, Thanks for the response but I was hoping for a more rigorous,
> formal explanation. In your first example you're using an initializer
> whereas in the second you're using assignment.
>
> I may be wrong but I feel the real explanation is more precise than,
> "...just how people in MS define the syntax".[/color]
Hi, buddy,

If I were you , I mean, if I am really serious about what the difference
is , I will write some sample code, compile it, and use
MSIL Disassembler (Ildasm.exe) to check whether they are compiled
differently.

re: Jagged and Multi-Dimensional Array Declaration Subtleties

Alan Foxmore <AFoxmore@yahoo.com> wrote:

<snip>
[color=blue]
> Specifically, the "new int[]" declarations are absolutely necessary to
> avoid a compiler error. If you remove the "new int[]" from the
> declaration you get this compiler error:
>
> "Array initializers can only be used in a variable or
> field initializer. Try using a new expression instead."
>
> I know that v is a multi-dimensional array and w is an "array of int
> array". So I understand the difference in semantics. But I can't
> articulate *why* there is a difference in the syntax.[/color]

Well, the syntax specifies exactly what's in the array in each case.
Apart from anything else, it makes it absolutely obvious whether you're
dealing with a multi-dimensional array or a jagged array.

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