Computer Programming Concepts and Visual Basic David I. Schneider

76 Computer Programming Concepts and Visual Basic
Private Sub Add(num1 As Single, num2 As Single)
‘Display numbers and their sum picResult.Print “The sum of”; num1; “and”;
num2; “is”; num1 + num2
End Sub
Private Sub ExplainPurpose()
‘Explain the task performed by the program
picResult.Print “This program displays sentences”
picResult.Print “identifying pairs of numbers and their sums.”
End Sub
[Run and then click the command button. The following is displayed in the picture box.]
This program displays sentences
identifying pairs of numbers and their sums.
The sum of 2 and 3 is 5
The sum of 4 and 6 is 10
The sum of 7 and 8 is 15
The variables num1 and num2 appearing in the Sub procedure Add are called parameters.
They are merely temporary place holders for the numbers passed to the Sub procedure;
their names are not important. The only essentials are their type, quantity, and order. In this
Add Sub procedure, the parameters must be numeric variables and there must be two of
them. For instance, the Sub procedure could have been written
Private Sub Add(this As Single, that As Single)
‘Display numbers and their sum
picResult.Print “The sum of”; this; “and”; that; “is”; this + that
End Sub
A string also can be passed to a Sub procedure. In this case, the receiving parameter in
the Sub procedure must be followed by the declaration As String.
EXAMPLE 4
The following program passes a string and two numbers to a Sub procedure. When the Sub procedure is
first called, the string parameter state is assigned the string constant “Hawaii”, and the numeric parameters
pop and area are assigned the numeric constants 1184000 and 6471, respectively. The Sub procedure
then uses these parameters to carry out the task of calculating the population density of Hawaii. The second
Call statement assigns different values to the parameters.
Private Sub cmdDisplay_Click()
‘Calculate the population densities of states
picDensity.Cls
Call CalculateDensity(“Hawaii”, 1184000, 6471)
Call CalculateDensity(“Alaska”, 607000, 591000)
End Sub
Object Property Setting
frmStates Caption State Demographics
cmdDisplay Caption Display Demographics
picDensity
Private Sub CalculateDensity(state As String, pop As Single, area As Single)
Dim rawDensity As Single, density As Single