Visual Basic.NET How to Program (PDF)

Chapter 7 Arrays 281
The program in Fig. 7.16 demonstrates the initialization of a rectangular array
(array1) and a jagged array (array2) in declarations and the use of nested For/Next
loops to traverse the arrays (i.e., to manipulate every array element).
The program declares two arrays in method Main. The allocation of array1 (line 14)
provides six initializers in two sublists. The first sublist initializes the first row (row 0) of the
array to the values 1, 2 and 3; the second sublist initializes the second row (row 1) of the array
to the values 4, 5 and 6. The declaration and allocation of array2 (line 17) create a jagged
array of 3 arrays (specified by the 2 in the first set of parentheses after keyword Integer).
Lines 18–20 initialize each subarray so that the first subarray contains the values 1 and 2, the
second contains the value 3 and the last contains the values 4, 5 and 6.
The nested For/Next structures in lines 24–31 append the elements of array1 to
string output. The nested For/Next structures traverse the arrays in two dimensions.
The outer For/Next structure traverses the rows; the inner For/Next structure traverses
the columns within a row. Each For/Next structure calls method GetUpperBound to
obtain the upper bound of the dimension it traverses. Notice that the dimensions are zerobased,
meaning the rows are dimension 0 and the columns are dimension 1.
1 ' Fig. 7.16: MultidimensionalArrays.vb
2 ' Initializing multi-dimensional arrays.
3
4 Imports System.Windows.Forms
5
6 Module modMultidimensionalArrays
7
8 Sub Main()
9 Dim output As String
10 Dim i, j As Integer
11
12 ' create rectangular two-dimensional array
13 Dim array1 As Integer(,)
14 array1 = New Integer(,) {{1, 2, 3}, {4, 5, 6}}
15
16 ' create jagged two-dimensional array
17 Dim array2 As Integer()() = New Integer(2)() {}
18
19 array2(0) = New Integer() {1, 2}
20 array2(1) = New Integer() {3}
21 array2(2) = New Integer() {4, 5, 6}
22
23 output = "Values in array1 by row are " & vbCrLf
24
25 For i = 0 To array1.GetUpperBound(0)
26
27 For j = 0 To array1.GetUpperBound(1)
28 output &= array1(i, j) & " "
29 Next
30
31 output &= vbCrLf
32 Next
33
Fig. Fig. 7.16 7.16 Initializing multidimensional arrays (part 1 of 2).