Resizing

Reducing Array Size

This can only be used when you have a one dimensional array

char[ ] myarray = new char[4]; 
myarray[0] = 'a';  
myarray[1] = 'b';  
myarray[2] = 'c';  
myarray[3] = 'd';  
System.Array.Resize(ref myarray, 2); 

Increasing Array Size

This can only be used when you have a one dimensional array

char[ ] myarray = new char[2]; 
myarray[0] = 'a';  
myarray[1] = 'b';  
System.Array.Resize<char>(ref myarray, 4); 
myarray[2] = 'c';  
myarray[3] = 'd';  

Resizing and Preserving

int[2] myarray; 
int[ ] temp = new int[4]; 
myarray[0] = 'a';  
myarray[1] = 'b';  
System.Array.Copy(myarray, temp, myarray.Length); 
myarray = temp 

ReDim - VB.Net

This is not possible in C#.
You can only use ReDim after static declaration in VB.NET.
Only the last dimension can be resized.

Dim myarray(6) As Integer 
Redim myarray(4) As Integer 

You cannot use ReDim as an array declaration in VB.NET

It is not possible to declare an array using the ReDim statement in .NET as it is in VBA.
You always have to declare the array before its dimension can be changed.

Dim aiArrayIntegers(10) As Integer 
ReDim aiArrayIntegers(20) 

Because the ReDim cannot be used to declare an array it no longer supports the "As" keyword.
The ReDim can only be used to change the number of elements in the last dimension of the array.
You can still use ReDim Preserve to keep the elements already in an array.

ReDim

The use of ReDim for allocating a new array is necessary because VB does not allow the use of "New" when working with arrays (except with the curly bracket notation).

Dim asArray(,) As String 
ReDim asArray(500,4) 

ReDim Preserve

Allows you to allocate a new array with new dimensions and copy all the elements from the old array to the new one in a single line of code

Dim asArray() As String = {"one","two","three"} 
ReDim Preserve asArray(10) 

What is actually happening here is that a brand new array is created and then the System.Array.Copy method is called
The equivalent in C# would be:

string[] asArray = {"one","two","three"}; 
string[] temp = new string[10]; 
System.Array.Copy(asArray, 0, temp, 0, asArray.Length); 
asArray = temp;