Visual Basic.NET How to Program (PDF)

248 Arrays Chapter 7
Let us examine array numberArray in Fig. 7.1 more closely. The name of the array
is numberArray. The 12 elements of the array are referred to as numberArray(0)
through numberArray(11). The value of numberArray(0) is -45, the value of
numberArray(1) is 6, the value of numberArray(2) is 0, the value of number-
Array(7) is 62 and the value of numberArray(11) is 78. Values stored in arrays can
be employed in various calculations and applications. For example, to determine the sum
of the values contained in the first three elements of array numberArray and then store
the result in variable sum, we would write
sum = numberArray(0) + numberArray(1) + numberArray(2)
To divide the value of the seventh element of array numberArray by 2 and assign the
result to the variable result, we would write
result = numberArray(6) \ 2
Common Programming Error 7.1
It is important to note the difference between the “seventh element of the array” and “array
element seven.” Array indices begin at 0, which means that the “seventh element of the array”
has the index 6, whereas “array element seven” has the index 7 and is actually the
eighth element of the array. This confusion is a common source of “off-by-one” errors. 7.1
Every array in Visual Basic “knows” its own length. The length of the array (i.e., 12
in this case) is determined by the following expression:
numberArray.Length
All arrays have access to the methods and properties of class System.Array, including
the Length property. For instance, method GetUpperBound returns the index of the
last element in the array. Method GetUpperBound takes one argument indicating a dimension
of the array. We discuss arrays with multiple dimensions in Section 7.9. For onedimensional
arrays, such as numberArray, the argument passed to GetUpperBound
is 0. For example, expression
numberArray.GetUpperBound(0)
returns 11. Notice that the value returned by method GetUpperBound is one less than
the value of the array’s Length property. Classes, objects and class methods are discussed
in detail in Chapter 8, Object-Based Programming.
7.3 Declaring and Allocating Arrays
Arrays occupy space in memory. The amount of memory required by an array depends on
the length of the array and the size of the data type of the elements in the array. The declaration
of an array creates a variable that can store a reference to an array but does not create
the array in memory. To declare an array, the programmer provides the array’s name and
data type. The following statement declares the array in Fig. 7.1:
Dim numberArray As Integer()