1. Arrays and Collections
By: Engr. Faisal ur Rehman
CE-105 Spring 2007

2. Array

3. Definition A variable storing multiple values
Called Matrix in Mathematics
Alternatives are:
Collection
Scalar variables

4. Array Terms ‘declaration Dim a(5) as integer Name same for all
Data
type
Name same for all
varaibles in this array
Index or subscript

5. Array Terms
Dimension: Specify the direction in which variable changes.
1d = n x Dim a(2) as double
2d = m x n Dim a(2,2) as double
3d = l x m x n Dim a(2,2,2) as double
Max 32 dimensions
More than 3 are rare
Rank: The Rank property returns the array's rank (number of dimensions).

6. Array Terms 2D
3x3 1D
3x1 3D
3x3x3 1 2
Dimensions

7. Array Terms
The GetLength method returns the length along the specified dimension
Def: Represents the number of elements in the specified dimension of the Array.
GetUpperBound (method): Gets the upper bound of the specified dimension in the Array
The Length property returns the total number of elements in the array.
The System.Array.Sort method sorts the elements of a one-dimensional array.

8. Array Terms
Jagged Array (Array of Array): Sometimes the data structure in your application is two-dimensional but not rectangular.
For example, you might have an array of months, each element of which is an array of days.
In such a case, you can use a jagged array instead of a multidimensional array.

9. Array Terms
The size of an array is the product of the lengths of all its dimensions.
It represents the total number of elements currently contained in the array.
Example:
Dim prices(3, 4, 5) As Long
The overall size of the array in variable prices is (3 + 1) x (4 + 1) x (5 + 1) = 120.
Determined by length property

10. Array Term Reallocates storage space for an array variable.
Used for dynamic array (change length at runtime) An array with no elements is also called a zero-length array
You can initialize an array at the same time you create it.
Dim P(3) as double() = New double() {2, 4, 5, 6}

11. Collections

12. Collection Collection is a data structure used for object
More efficient in storing items than an array.

13. Collection Index and Key Values
Instances of the Visual Basic Collection class allow you to access an item using either:
a numeric index
-or-
a String key.
You can add items to Visual Basic Collection objects either with or without specifying a key.
If you add an item without a key, you must use its numeric index to access it.
Item of Collection:
A single / element of collection

14. Collection Example Dim birthdays As New Collection()
birthdays.Add(New DateTime(2001, 1, 12), "Bill")
birthdays.Add(New DateTime(2001, 1, 13), "Joe")
birthdays.Add(New DateTime(2001, 1, 14), "Mike")
birthdays.Add(New DateTime(2001, 1, 15), "Pete")
Dim aBirthday As DateTime
aBirthday = birthdays.Item("Bill")
MsgBox(CStr(aBirthday))
aBirthday = birthdays("Bill")
End Sub

15. Q & A

16. Q & A (Assignment) Define: Array Size of Array Length of Array
Rank of Array
Dimension of Array
System.array.sort
Jagged Array
Dynamic array
Collection
Key
Index
Item

17. Thanks