Computer Programming Concepts and Visual Basic David I. Schneider

82 Computer Programming Concepts and Visual Basic
EXAMPLE 2
The following variation of the addition program from the previous section uses a Sub procedure to acquire
the input. The variables x and y are not assigned values prior to the execution of the first Call statement.
Therefore, before the Call statement is executed, they have the value 0. After the Call statement is executed,
however, they have the values 2 and 3. These values then are passed by the second Call statement
to the Sub procedure Add.
Private Sub cmdCompute_Click()
Dim x As Single, y As Single
‘Display the sum of the two numbers
Call GetNumbers(x, y)
Call Add(x, y)
End Sub
Object Property Setting
frmAdd Caption Add Two Numbers
lblFirstNum Caption First Number
txtFirstNum Text (blank)
lblSecondNum Caption Second Number
txtSecondNum Text (blank)
cmdCompute Caption Compute Sum
picResult
Private Sub Add(num1 As Single, num2 As Single)
Dim sum As Single
‘Display numbers and their sum
picResult.Cls
sum = num1 + num2
picResult.Print “The sum of”; num1; “and”; num2; “is”; sum
End Sub
Private Sub GetNumbers(num1 As Single, num2 As Single)
‘Record the two numbers in the text boxes
num1 = Val(txtFirstNum.Text)
num2 = Val(txtSecondNum.Text)
End Sub
[Run, type 2 and 3 into the text boxes, and then click the command button.]
In most situations, a variable with no preassigned value is used as an argument of a Call
statement for the sole purpose of carrying back a value from the Sub procedure.
EXAMPLE 3
The following variation of Example 2 allows the cmdCompute_Click event procedure to be written in the
input-process-output style.
Private Sub cmdCompute_Click()
Dim x As Single, y As Single, s As Single
‘Display the sum of two numbers
Call GetNumbers(x, y)