CS0004: Introduction to Programming

1. CS0004: Introduction to Programming Function Procedures

2. Review • General Form of an If/Else Block… If condition Then some code Else some other code End If • General Form of a Select Case Block Select Case selector Case valueList1 action1 Case valueList2 action2 Case Else actionOfLastResort End Select

3. Review • A value list can be a…(4 things) • Literal • Variable • Expression • Range • What property holds whether a radio button or check box is checked? • Checked

4. Function Procedures • Functions are used in programming to break complex problems into smaller ones • We have encountered built-in functions in VB before • Int(param1) • FormatNumber(param1,param2) • These functions output a value to where they are used. • When a function outputs a value, it is said to return a value. • When a function is used, it is said to be called. • You can pass input to a function by supplying it with arguments. • Arguments are the values you pass to a function • Parameters are the local variables used in the function definition.

5. Function Procedures • We can define our own functions: • General Form: FunctionFunctionName (ByValvar1As Type, ByValvar2As Type) As ReturnDataType … some code … Returnexpression End Function • FunctionName is the name of the function • var1 and var2 are the names of the parameters • The Types following var1 and var2 tell what type the parameters are • ReturnDataType is the type of the value that the function returns • The expression in Returnexpressionis what value is returned by the function.

6. Function Example 1 • New Topics: • Programmer Defined Function • Parameters/arguments • Return Statement • Function Call

7. Function Procedures • Notes: • The code for the function is called the function definition. • When calling a function, you must supply it with the same number of arguments as parameters defined in the function definition. • You can create functions with no parameters. Just leave the parentheses empty when defining the function. • A function MUST return a value. • Function names in VB: • Typically are camel case with first letter capitalized. • Follow the same naming rules as variables • Should be a verb that describe what the function does

8. Function Example 2 • New Topics: • Multiple Parameters/Arguments

9. Scope • Scope refers to where a variable can be used (seen). • Scope is usually defined by where it was declared. • A variable declared in a function or event procedure can ONLY be used in the function or event procedure where it was declared. • A variable declared inside of a class, but not in any of its procedures can be used anywhere in the class, including in any of its procedures. • Parameters can be used ONLY in the function they belong to.

10. Scope • Example: Public Class frmMain Dim var1 As Integer Function someFunction(ByVal x As Double, ByVal yAs Double) As Double Dim var2 As String … End Function Function otherFunction(ByValx As String, ByVal y As String) As Double Dim var3 As String … End Function End Class

11. Function Documentation • You should document EVERY function you write: ‘ Function Name: The name of the function ‘ Returns: Return type and brief description of what it ‘ is ‘ Parameters: Types and brief descriptions of what they are ‘ Description: Brief description of what the function does