Computer Programming Concepts and Visual Basic David I. Schneider

162 Computer Programming Concepts and Visual Basic
into a short loop. A shorthand notation for the many related variables would be welcome. It
would be nice if we could just write
For i = 1 To 30
Input #1, studenti, scorei
Next i
Of course, this will not work. Visual Basic will treat studenti and scorei as two variables and
keep reassigning new values to them. At the end of the loop they will have the values of the
thirtieth student.
Visual Basic provides a data structure called an array that lets us do what we tried to
accomplish in the loop. The variable names will be similar to those in the Input # statement.
They will be
student(1), student(2), student(3), ..., student(30)
and
score(1), score(2), score(3), ..., score(30).
We refer to these collections of variables as the array variables student( ) and score( ). The numbers
inside the parentheses of the individual variables are called subscripts, and each individual
variable is called a subscripted variable or element. For instance, student(3) is the third subscripted
variable of the array student( ), and score( ) is the 20th subscripted variable of the array
score( ). The elements of an array are assigned successive memory locations. Figure 6-1 shows
the memory locations for the array score( ).
FIGURE 6-1 The Array Score( )
Array variables have the same kinds of names as simple variables. If arrayName is the
name of an array variable and n is a whole number, then the statement
Dim arrayName(1 To n) As varType
placed in the (Declarations) section of (General) reserves space in memory to hold the values
of the subscripted variables arrayName(1), arrayName(2), arrayName(3), . . . , arrayName(n).
(Recall from Section 3.1 that the (Declarations) section of (General) is accessed from any
code window by selecting these values in the Object and Procedure boxes.) The spread of the
subscripts specified by the Dim statement is called the range of the array, and the Dim statement
is said to dimension the array. The subscripted variables will all have the same data type;
namely, the type specified by varType. For instance, they could be all String variables or all
Integer variables. In particular, the statements
Dim student(1 To 30) As String
Dim score(1 To 30) As Integer
dimension the arrays needed for the preceding program.
As with any variable created in the (Declarations) section of (General), these array variables
are form-level as discussed in Section 3. Recall that form-level variables can be
accessed from any procedure in the program and continue to exist and retain their values as
long as the program is running.
Values can be assigned to subscripted variables with assignment statements and displayed
with Print methods. The statement
Dim score(1 To 30) As Integer