Terminology and Concepts
One-Dimensional Arrays Two-Dimensional Arrays
Arrays are data structures
They contain data - variables - of same type (Integer, Double, for example)
The size of an array (how many elements if contains) is fixed once it is created
An array named c with 12 elements
c is the name of the array
Position number is in parentheses - it must be positive integer - first element has position
number 0
c.Length is a method that returns the length of array c - which is 12 in this case
c.GetUpperBound is a method that returns 1 less than the value of c.Length. The parameter 0
indicates that it is a one-dimensional array - we discuss multiple dimensions later
•Declaring and Creating Arrays
–Arrays are objects that occupy memory
–Either of the following statements can be used to declare an array
• Dim c As Integer()
• Dim c() As Integer
–Created dynamically with keyword New
Dim c As Integer() = New Integer(11){}
-Equivalent to:
Dim c As Integer() ‘ declare array variable
c = New
Integer(11){} ‘ create array
-
•Initializer List
–Required braces {}
–Specifies initial values of the elements in the array
–When the initializer list is empty, the elements in the array are initialized to the default value for the type of elements of the array
–The initializer list can contain a comma-separated list specifying the initial values of the elements in the array
•Example
- Dim c As Integer() = New Integer() {1, 2, 3, 4}
Summary
An array is a group
of variables (called elements) that all have the same data type. The same array cannot hold
both integers and doubles, for example.
To refer to a
specific element of an array, specify the name of the array and its position number.
Every array begins
with the zeroth element (element 0).
The position number
in parentheses is called an index or a subscript.
Every array in VB
knows its own length. The length of an array
named A is returned by the expression A.length
Method GetUpperBound
returns the index of the last element in the array. Note that A.GetUpperBound
is 1 less than A.length
To declare an array,
provide the array's name and type. For example
Dim A as Integer().
The parentheses that
follow the type indicate that A is an array. Otherwise it would be
considered a variable.
The declaration of an
array creates a variable that can store a reference to any array but does not actually create the
array in memory.
Before an array can
be used you must specify the size and allocate memory for the array using the keyword New.
When the initializer
list is empty, the elements in the array are initialized to the default value
for the type of the elements
in the array.
To pass an array to a
method, specify the name of the array without using parentheses.
For a method to
receive an array through its parameter list, the parameter must specify that an array is to be
received.
Arrays are always passed by reference.
To pass an array
element to a method, use the indexed name of the array element as an argument.
For a method to
receive an array element through its parameter list, the parameter must specify that an array
element is to be received.
The For loop is used
to iterate through the elements of an array.