Microsoft Visual Basic 2010 Step by Step eBook

258 Part II Programming Fundamentals

statement that places the final calculation of the function in FunctionName. For example, the

Function procedure TotalTax computes the state and city taxes for an item and then assigns

the result to the TotalTax name, as shown here:

Function TotalTax(ByVal Cost as Single) As Single

Dim StateTax, CityTax As Single

StateTax = Cost * 0.05 'State tax is 5%

CityTax = Cost * 0.015 'City tax is 1.5%

TotalTax = StateTax + CityTax

End Function

Alternatively, you can return a value to the calling procedure by using the Return statement,

as shown in the following function declaration:

Function TotalTax(ByVal Cost as Single) As Single

Dim StateTax, CityTax As Single

StateTax = Cost * 0.05 'State tax is 5%

CityTax = Cost * 0.015 'City tax is 1.5%

Return StateTax + CityTax

End Function

I’ll use the Return syntax most often in this book, but you can use either mechanism for re-

turning data from a function.

Calling a Function Procedure

To call the TotalTax function in an event procedure, you use a statement similar to the

following:

lblTaxes.Text = TotalTax(500)

This statement computes the total taxes required for a $500 item and then assigns the result

to the Text property of the lblTaxes object. The TotalTax function can also take a variable as

an argument, as shown in the following statements:

Dim TotalCost, SalesPrice As Single

SalesPrice = 500

TotalCost = SalesPrice + TotalTax(SalesPrice)

The last statement uses the TotalTax function to determine the taxes for the number in the

SalesPrice variable and then adds the computed tax to SalesPrice to get the total cost of an

item. See how much clearer the code is when a function is used?

Using a Function to Perform a Calculation

In the following exercise, you’ll add a function to the Track Wins program to calculate the win

rate in the game—in other words, the percentage of spins in which one or more 7s appear.

To perform the calculation, you’ll add a function named HitRate and a public variable named