Visual Basic.NET How to Program (PDF)

Chapter 7 Arrays 289
13 For Each grade In gradeArray
14
15 If grade < lowGrade Then
16 lowGrade = grade
17 End If
18
19 Next
20
21 Console.WriteLine("The minimum grade is: {0}", lowGrade)
22 End Sub ' Main
23
24 End Module ' modForEach
The minimum grade is: 68
Fig. Fig. 7.19 7.19 Using For Each/Next with an array (part 2 of 2).
The program behaves similarly to procedure Minimum of Fig. 7.17, but consolidates
the nested For structures into one For Each structure. The header of the For Each repetition
structure (line 13) specifies a variable, grade, and an array, gradeArray. The
For Each/Next structure iterates through all the elements in gradeArray, sequentially
assigning each value to variable grade. The values are compared to variable lowGrade
(line 15), which stores the lowest grade in the array.
For rectangular arrays, the repetition of the For Each/Next structure begins with the
element whose indices are all zero, then iterates through all possible combinations of
indices, incrementing the rightmost index first. When the rightmost index reaches its upper
bound, it is reset to zero, and the index to the left of it is incremented by 1. In this case,
grade takes the values as they are ordered in the initializer list in line 8. When all the
grades have been processed, lowGrade is displayed.
Although many array calculations are handled best with a counter, For Each is useful
when the indices of the elements are not important. For Each/Next particularly is useful
for looping through arrays of objects, as we discuss in Chapter 10, Object-Oriented Programming:
Polymorphism
In this chapter, we showed how to program with arrays. We mentioned that Visual
Basic .NET arrays are objects. In Chapter 8, Object-Based Programming, we show how to
create classes, which are essentially the “blueprints” from which objects are instantiated
(i.e., created).
SUMMARY
An array is a group of contiguous memory locations that have the same name and are of the same
type.
The first element in every array is th e zeroth element (i.e., element 0).
The position number in parentheses more formally is called the index (or the subscript). An index
must be an integer or an integer expression.
All arrays have access to the methods and properties of class System.Array, including the
GetUpperBound method and the Length property.
To reference the ith element of an array, use i - 1 as the index.