Visual Basic.NET How to Program (PDF)

Chapter 7 Arrays 263
84 element *= 2
85 output &= vbCrLf & "Value calculated in " & _
86 "ModifyElementByRef: " & element
87 End Sub ' ModifyElementByRef
88
89 End Module ' modPassArray
Fig. Fig. 7.8 7.8 Passing arrays and individual array elements to procedures (part 3 of 3).
The For/Next structure on lines 18–20 appends the five elements of integer array
array1 (line 10) to String output. Line 22 passes array1 to procedure ModifyArray
(line 58), which then multiplies each element by 2 (line 62). To illustrate that
array1’s elements were modified in the called procedure (i.e., as enabled by passing by
reference), the For/Next structure in lines 28–30 appends the five elements of array1
to output. As the screen capture indicates, the elements of array1 are indeed modified
by ModifyArray.
To show the value of array1(3) before the call to ModifyElementByVal, lines
32–35 append the value of array1(3) to String output. Line 38 invokes procedure
ModifyElementByVal and passes array1(3). When array1(3) is passed by
value, the Integer value in the fourth position of array array1 (now an 8) is copied
and is passed to procedure ModifyElementByVal, where it becomes the value of argument
element. Procedure ModifyElementByVal then multiplies element by 2
(line 73). The parameter of ModifyElementByVal is a local variable that is destroyed
when the procedure terminates. Thus, when control is returned to Main, the unmodified
value of array1(3) is appended to the string variable output (lines 40–41).
Lines 43–51 demonstrate the effects of procedure ModifyElementByRef (lines
80–87). This procedure performs the same calculation as ModifyElementByVal, multiplying
element by 2. In this case, array1(3) is passed by reference, meaning the
value of array1(3) appended to output (lines 50–51) is the same as the value calculated
in the procedure.
Common Programming Error 7.3
In the passing of an array to a procedure, including an empty pair of parentheses after the
array name is a syntax error. 7.3