Passing Variable Number of Parameters

When calling a procedure or function method, you are allowed to pass a variable number of parameters. If a procedure or function might receive a variable number of parameters, you need to check how many parameters were actually passed and only use the parameters that were passed.

Num_Arguments

You can check for the number of parameters passed by using the Num_Arguments variable.

In the following example, the procedure ApplyDiscount checks to see if one or two parameters were passed and adjusts its logic accordingly:

Class cMyButton is a Button
    Procedure ApplyDiscount number nAmount integer iPercent
        Number nDiscount

        If (Num_Arguments = 2) Begin
            Move (nAmount / 100 * iPercent) to nDiscount
        End
        Else Begin
            // If percent not passed, apply standard discount of 10%
            Move (nAmount * .10) to nDiscount
        End

        Send ShowDiscount nDiscount
    End_Procedure

    Procedure OnClick
        Send ApplyDiscount nAmount 50 // Apply 50% discount
        Send ApplyDiscount nAmount     // Apply standard discount
    End_Procedure
End_Class

In the above example, ApplyDiscount could be successfully called by passing it either 1 or 2 parameters.

If a parameter is not passed, the variable used for that parameter cannot be used in the procedure or function – although it is named, it does not exist. For example, the following code would generate a runtime error when passed a single parameter:

Procedure ApplyDiscount number nAmount integer iPercent
    Number nDiscount

    If (Num_Arguments = 1) Begin
        Move 10 to iPercent // This will not work!
    End

    Move (nAmount / 100 * iPercent) to nDiscount
    Send ShowDiscount nDiscount
End_Procedure

In the above example, you may not move a value to iPercent because the variable is not defined if the parameter is not passed. The proper code for this sample would be:

Procedure ApplyDiscount number nAmount integer iPercent
    Number nDiscount
    Integer iApplyPercent

    If (Num_Arguments = 1) Begin
        Move 10 to iApplyPercent
    End
    Else Begin
        Move iPercent to iApplyPercent
    End

    Move (nAmount / 100 * iApplyPercent) to nDiscount
    Send ShowDiscount nDiscount
End_Procedure

Note that this technique is also supported for global procedures and functions.