 ◦ ◦ ◦ “Regular” variable Holds a single value For example Dim Student1 as String Dim Student2 as String Dim Student3 as String … Dim Student n as String If you have 10 students, you can also have variables representing students’ grades   You can total up and average these grades for the “class” of 10 students ClassAvg = StudentGrade1 + StudentGrade2 + … What happens if you have 1000 students?

  An array is a set of values that are logically related to each other ◦ ◦ ◦ ◦ Monthly rainfall for the year Number of students in each grade in a grade school Number of employees in each department of an organization ◦ ◦ Employees within a single department Arrays let us refer to values by the same name Individual items are referred to as number to indicate we want which elements and we use a specific element in the array Element number is called the “index” or “subscript”

 ◦ ◦ Dim Students(6) as Integer Creates an array using the name “Students” with “containers” called “elements” Elements start number at “0”  7 elements exist in the Students array

  ◦ Assignment statements are used to place a value into a specific element We just need to specify which element ◦ Students(4) = 18  Places the value of 18 into the 5 th counting at 0) of the array element (we start Retrieving a value is as simple as specifying the element number System.Console.WriteLine( Cstr( Students(4) ) )

 Assuming that we have an array “Students” which represents the grades kindergarten through 6 th grade (kindergarten being grade “0”) Dim Students(6) as Integer Students(0)=11 Students(1)=14 Students(2)=17 Students(3)=11 Students(4)=19 Students(5)=21 Students(6)=10 Students 0 11 1 14 2 17 3 11 4 19 5 21 6 10

 We can get the total number of students in the school by adding the values in all the elements together ◦ TotalStudents = Students(0) + Students(1) + Students(2) + Students(3) + Students(4) + Students(5) + Students(6) Typical processing of an array is by using a “LOOP” Dim Grade,TotalStudents as Integer TotalStudents = 0 For Grade = 0 to 6 TotalStudents = TotalStudents + Students(Grade) Next Grade Students 0 1 2 3 4 5 6 11 14 17 11 19 21 10

  The elements in an array are of the same data type ◦ Integer ◦ ◦ ◦ ◦ String Boolean Char Etc You cannot exceed the subscript range of the array ◦ In “Students() ” you cannot refer to an element that does not exist   Typically done by “messing up” the loop counter Produces a “run time” error For Grade = 0 to TotalStudent=TotalStudents + Students(Grade) Next Grade

Dim Students as Integer( ) = New Integer(6) {11,14,17,11,19,21,10} Integer( ) is the data type (array of integers) Students 0 11 1 14 2 17 3 11 4 19 5 21 6 10

  If you decide to include up to the 8 th ReDim Students(8) Anything in the array will be lost!

Grade

  ◦ ◦ Suppose we have a company with 100 employees   Each employee has an Employee ID # A “whole counting number” We wish to keep track of his/her salary Could be a decimal Create an array to hold this information Dim Employee(2,100) as Single    Create a 3 x 101 matrix  Note: data is of type “single” even though employee number is an integer  Salary is a decimal type (non-integer), so employee # 21 is 21.00 in the array We don’t have to use the “0 th ” row or column, they can remain empty Alternatively Dim Employee(1,99) as Single

  ◦ Add as many pairs of parentheses after the variable name as there are levels of nested arrays ◦ Dim x as Integer( ) ( ) = New Integer( ) ( ) { } Add the same number of paired parentheses to the “New” clause You don’t need more that one pair of braces if you’re not giving an element values

 ◦ Two dimensional, but not “rectangular” Array of months   Each element is an array of days Dim sales()() As Double = New Double(11)( ) { } Dim month As Integer Dim days As Integer For month = 0 To 11 days = DateTime.DaysInMonth(Year(Now), month + 1) sales(month) = New Double(days - 1) {} Next month declares an array variable to hold an array of arrays with elements of the Double Data Type  Each element or the array “sales” is itself an array representing a month  Each month holds values for each day in that month

    ◦ Technically you cannot do this Arrays are of the same type The type we will use is “Object” Dim x as Object( ) = New Object( ) { } Example Dim employeeData(3) as Object employeeData(0) = “John Doe” employeeData(1) = “13 East North Rd.” employeeData(2) = 22 employeeData(3) = #04/01/1982# Age = CInt( employeeData(2) ) DOB = CDate( employeeData(3) ) Negative performance consideration

   ◦ ◦ ◦ ◦ Errors in declaring / initializing Supplying the “new” clause after specifying dimension lengths Omitting “new” when specifying element values Using the “new” clause without braces Out of bounds Going beyond the upper or lower bounds of the dimensions ◦ ◦ Specifying dimension GetLowerBound “0-based” Lbound and and Ubound GetUpperBound are “1-based” methods are