You can create your own customized functions easily in VB6.
The structure of a function is as follows:
Public Function functionName(Arg As dataType,.......) As dataType ' Public means applicable to whole project
Private Function functionName(Arg As dataType,.......) As dataType ' Private means applicable to a module
In this example, a user can calculate the future value of a certain amount of money he has today based on the interest rate and the number of years from now, supposing he will invest this amount of money somewhere .The calculation is based on the compound interest rate.
Public Function FV(PV As Variant, i As Variant, n As Variant) As Variant 'Formula to calculate Future Value(FV) 'PV denotes Present Value FV = PV * (1 + i / 100) ^ n End Function Private Sub compute_Click() 'This procedure will calculate Future Value Dim FutureVal As Variant Dim PresentVal As Variant Dim interest As Variant Dim period As Variant PresentVal = PV.Text interest = rate.Text period = years.Text 'calling the function FutureVal = FV(PresentVal, interest, period) MsgBox ("The Future Value is" & FutureVal) End Sub
The following program will automatically compute examination grades based on the marks that a student obtained. The code is shown below:
Public Function grade(mark As Variant) As String Select Case mark Case Is >= 80 grade ="A" Case Is>= 70 grade ="B" Case Is >= 60 grade ="C" Case Is >= 50 grade ="D" Case Is >= 40 grade ="E" Case Else grade ="F" End Select End Function
Private Sub compute_Click() grading.Caption = grade(mark) End Sub
A sub procedure(also call subroutine) is a procedure that is called from the main procedure to perform a specific task. It is different from function in the sense that it does not return a value as a function does.A sub procedure is usually used to accept input from the user, display information, print information, manipulate properties or perform some other tasks. It is a program code by itself and it is not an event procedure because it is not associated with a runtime procedure . It is called by other code whenever it is required to perform a certain task. Sub procedures help to make programs smaller and seamless to manage. A sub procedure begins with a Sub ProcedureName keyword and ends with an End Sub keyword.
The structure of a sub procedure is as follows:
Sub ProcedureName (arguments) Statements End Sub
In this example, we create a sub procedure to sum up two values that are specified by the arguments . The main program can reference a procedure by using its name together with the arguments in the parentheses.
Private Sub cmdCal_Click() Dim x As Single, y As Single x = Val(TxtNum1.Text) y = Val(TxtNum2.Text) sum x, y End Sub Sub sum(a As Single, b As Single) MsgBox ("sum=" & a + b) End Sub
Running the program produces a message boxes as shown in Figure 14.3a and Figure 14.3b
This program determines buying decision based on shoe' size and its price. In this program, we create a sub procedure known as buy_decision that has two arguments, size and price. A boolean variable buy is included to help in decision making. It takes a value of true or false. If the size and price entered fufilled the requirement via the If..Then...Else statement, buy is assigned a value of true, else it is assigned a value of false.
Public Sub buy_decision(size As Integer, price As Single) Dim buy As Boolean If size >= 7 And price <= 200 Then buy = True MsgBox ("Buy") Else: buy = False MsgBox ("Don't Buy") End If End Sub Private Sub CmdDecide_Click() Dim shoe_size As Integer, shoe_price As Single shoe_size = TxtX.Text shoe_price = TxtY.Text buy_decision shoe_size, shoe_price End Sub