18.6. Method Arguments

Methods can take any number of parameters.^[*] The parameter list follows the method name and is enclosed in parentheses. Each parameter's type is identified after the name of the parameter.

^[*] The terms "argument" and "parameter" are used interchangeably in this book, though some programmers prefer to differentiatie between the parameter declaration and the arguments passed in when the method is invoked.

For example, the following declaration defines a sub named MyMethod that takes two parameters: an Integer and a Button:

 Sub MyMethod (firstParam as Integer, secondParam as Button)   ' ... End Sub 

Within the body of the method, the parameters act as local variables, as if you had declared them in the body of the method and initialized them with the values passed in. Example 18-2 illustrates how you pass values into a method, in this case, values of type Integer and Single.

Example 18-2. Passing parameters

 Public Class TestClass    Sub SomeMethod( _       ByVal firstParam As Integer, _       ByVal secondParam As Single)       Console.WriteLine( _          "Here are the parameters received: {0}, {1}", _          firstParam, secondParam)    End Sub End Class Module Module1    Sub Main(  )       Dim howManyPeople As Integer = 5       Dim pi As Single = 3.14F       Dim tc As New TestClass(  )       tc.SomeMethod(howManyPeople, pi)    End Sub End Module Output: Here are the parameters received: 5, 3.14 

Visual Studio will mark your parameters as ByVal:

 ByVal firstParam As Integer 

This indicates that the parameter is passed "by value" that is, a copy is made.

Note that, if Strict is On, (which is should be) when you pass in a Single with a decimal part (3.14) you must append the letter f (3.14f) to signal to the compiler that the value is a Single, and not a Double.

The method SomeMethod( ) takes an Integer and a Single and displays them using Console.WriteLine( ). The parameters, firstParam and secondParam, are treated as local variables within SomeMethod( ).

In the calling method (Main( )), two local variables (howManyPeople and pi) are created and initialized. These variables are passed as the arguments to SomeMethod( ). The compiler maps howManyPeople to firstParam and pi to secondParam, based on their relative positions in the parameter list.