Multidimensional Array vs

Question

double     ServicePoint   new double 10  9       lt -- gives an error  1  double    ServicePoint   new double 10 9       lt -- ok  2    What s their difference   1  yields an error  what s the reason   And  double d   new double 9  ServicePoint 0    d    using  2  will prompt an error  Why

User · Answer

In the first instance you are trying to create what is called a jagged array.

double[][] ServicePoint = new double[10][9].

The above statement would have worked if it was defined like below.

double[][] ServicePoint = new double[10][]

what this means is you are creating an array of size 10 ,that can store 10 differently sized arrays inside it.In simple terms an Array of arrays.see the below image,which signifies a jagged array.

enter image description here

http://msdn.microsoft.com/en-us/library/2s05feca(v=vs.80).aspx

The second one is basically a two dimensional array and the syntax is correct and acceptable.

  double[,] ServicePoint = new double[10,9];//<-ok (2)

And to access or modify a two dimensional array you have to pass both the dimensions,but in your case you are passing just a single dimension,thats why the error

Correct usage would be

ServicePoint[0][2] ,Refers to an item on the first row ,third column.

Pictorial rep of your two dimensional array

enter image description here

User · Answer

double    is a 2d array  matrix  while double     is an array of arrays  jagged arrays  and the syntax is   double     ServicePoint   new double 10

User · Answer

double     are called jagged arrays   The inner dimensions aren   t specified in the declaration  Unlike a rectangular array  each inner array can be an arbitrary length  Each inner array is implicitly initialized to null rather than an empty array  Each inner array must be created manually  Reference  C  4 0 in nutshell The definitive Reference   for  int i   0  i  lt  matrix Length  i          matrix i    new int  3      Create inner array     for  int j   0  j  lt  matrix i  Length  j            matrix i  j    i   3   j      double    are called rectangular arrays  which are declared using commas to separate each dimension  The following piece of code declares a rectangular 3-by-3 two-dimensional array  initializing it with numbers from 0 to 8   int     matrix   new int  3  3   for  int i   0  i  lt  matrix GetLength 0   i        for  int j   0  j  lt  matrix GetLength 1   j            matrix  i  j    i   3   j

User · Answer

One is an array of arrays  and one is a 2d array   The former can be jagged  the latter is uniform   That is  a double     can validly be   double     x   new double 5      x 0    new double 10   x 1    new double 5   x 2    new double 3   x 3    new double 100   x 4    new double 1     Because each entry in the array is a reference to an array of double  With a jagged array  you can do an assignment to an array like you want in your second example   x 0    new double 13     On the second item  because it is a uniform 2d array  you can t assign a 1d array to a row or column  because you must index both the row and column  which gets you down to a single double   double    ServicePoint   new double 10 9    ServicePoint 0         lt -- meaningless  a 2d array can t use just one index    UPDATE   To clarify based on your question  the reason your  1 had a syntax error is because you had this   double     ServicePoint   new double 10  9     And you can t specify the second index at the time of construction   The key is that ServicePoint is not a 2d array  but an 1d array  of arrays  and thus since you are creating a 1d array  of arrays   you specify only one index   double     ServicePoint   new double 10       Then  when you create each item in the array  each of those are also arrays  so then you can specify their dimensions  which can be different  hence the term jagged array    ServicePoint 0    new double 13   ServicePoint 1    new double 20     Hope that helps

User · Answer

double     is an array of arrays and double    is a matrix  If you want to initialize an array of array  you will need to do this   double     ServicePoint   new double 10    for var i 0 i lt ServicePoint Length i        ServicePoint i    new double 9     Take in account that using arrays of arrays will let you have arrays of different lengths   ServicePoint 0    new double 10   ServicePoint 1    new double 3   ServicePoint 2    new double 5     and so on

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