Thread: how to init 2d array ?

hi all~

i'm new to C# and get confused this moment with 2d array initialization. i declared 2d array like this:

Code:

int[,] = new int[2, 1];

and how to initialize them with the same line ?

If you need to do so, you can initialize n-dimensional arrays like this:

PHP Code:

int[,] array = new int[2,3] {{1,2,3},{5,6,7}}; 


Originally Posted by nvoigt

If you need to do so, you can initialize n-dimensional arrays like this:

PHP Code:

int[,] array = new int[2,3] {{1,2,3},{5,6,7}}; 


thanx but i tried it and it didnt work ???

it should work. if it does not, then something else is wrong with your program.

here is a quick little program using that same code that nv posted:

Code:

using System;

class myprog
{
	static void Main ( string [] args )
	{
		int[,] array = new int[2,3] {{1,2,3},{5,6,7}};

		for ( int k = 0; k < 2; k++ )
			for ( int j = 0; j < 3; j++ )
				Console.WriteLine ( array[k,j] );
	}
}

ok i succeed in establishing the 2d array but failed when output it ??? here is my code(an .aspx file):

Code:

<%
	int[,] arr = new int[2, 3] {{1, 2, 3}, {4, 5, 6}};
	Response.Write(arr[0][0]);
%>

the compiler hint the error happened at the line which i Response.Write the result, what's wrong there ???

So what kind of error is it ? Can you post the exact error message please ?
If it's a runtime error, can you catch the exception and output the stack trace and error message please ?
( Both are properties of the exception object )

Edit:
Also, make sure you don't mix jagged and rectangular arrays.

array[][] is not the same as array[,]

Originally Posted by black

ok i succeed in establishing the 2d array but failed when output it ??? here is my code(an .aspx file):

Code:

<%
	int[,] arr = new int[2, 3] {{1, 2, 3}, {4, 5, 6}};
	Response.Write(arr[0][0]);
%>

the compiler hint the error happened at the line which i Response.Write the result, what's wrong there ???

to my surprise i found this would work:

Code:

Response.Write(arr[0, 0]);

cant we get value with the format like arr[0][0] any more ???

I see, you found it while I was editing my post

int [,] is a rectangular array, that is an array that has n dimensions.

int[][] is a jagged array, that is an array of arrays.

Originally Posted by nvoigt

I see, you found it while I was editing my post

int [,] is a rectangular array, that is an array that has n dimensions.

int[][] is a jagged array, that is an array of arrays.

thanx but... what's the difference between them ? i remembered C++ and C also index multi dimention array value with something like arr[1][2][3], really confused...

In a rectangular array, each column and row has to have the same size like this: ( array[4,7] )

0123456
0123456
0123456
0123456

while a jagged array is an array of arrays, where you have two different dimensions and as such you can put another array length into each line: ( array[4][] )

0123456789
01234
01234567
0123456

thanx nvoigt, and i read the part for jagged arraay from C# primer, which has the same remarks

but i'd really used to deal with multi arrays like this arr[1][2], can rectangle array apply this way or is there any substitute for arr[1, 2] ?

Well, if you do some initialization work yourself and take a slight performance loss into account ( no biggie with a garbage collected language anyway ) you can build your 2d aray as a jagged array of same size arrays and use the [][] notation anyway, but it's confusing for readers and a lot of extra work just to avoid the comma

Originally Posted by nvoigt

Well, if you do some initialization work yourself and take a slight performance loss into account ( no biggie with a garbage collected language anyway ) you can build your 2d aray as a jagged array of same size arrays and use the [][] notation anyway, but it's confusing for readers and a lot of extra work just to avoid the comma

thanx nvoigt i think i would learn this new feature to make performance better

Sorry, I don't speak french. Maybe you could rephrase your question in english ( or german so I can translate ) ?