VBScript

1. VBScript Session 7

2. What we learn last session? • Interacting in VBScript • VBScript constants groups.

3. Subjects for session 7 • VBScript procedures. • Sub procedures. • Function Procedures. • Getting data into and out of procedures • Call statement. • Arguments ByVal and ByRef

4. VBScript Procedures • In VBScript, there are two kinds of procedures; • the Sub procedure and the Function procedure.

5. VBScript Procedures Sub Procedures • A Sub procedure is a series of VBScript statements (enclosed by Sub and EndSub statements) that perform actions but don't return a value. • A Sub procedure can take arguments (constants, variables, or expressions that are passed by a calling procedure). • If a Sub procedure has no arguments, its Sub statement must include an empty set of parentheses ().

6. VBScript Procedures Function Procedures • A Function procedure is a series of VBScript statements enclosed by the Function and End Function statements. • A Function procedure is similar to a Sub procedure, but can also return a value. • If a Function procedure has no arguments, the Function statement must include an empty set of parentheses. • A Function returns a value by assigning a value to its name in one or more statements of the procedure. • The return type of a Function is always a Variant. • The MsgBox and InputBox, are VBScript functions.

7. VBScript Procedures Sub and Function Procedures • If not explicitly specified using either Public or Private, Sub procedures are public by default, that is, they are visible to all other procedures in your script. • The value of local variables in a Sub or a Function procedure is not preserved between calls to the procedure. • You can't define a Sub procedure inside any other procedure. • The Exit Sub, Exit Functionstatement causes an immediate exit from a Sub or Function procedure. • Any number of ExitSub or ExitFunction statements can appear anywhere in a Sub or Function procedure.

8. VBScript Procedures Sub Procedures • Like a Function procedure, a Sub procedure is a separate procedure that can take arguments, perform a series of statements, and change the value of its arguments. • However, unlike a Function procedure, which returns a value, a Sub procedure can't be used in an expression • You call a Sub procedure using the procedure name followed by the argument list. • CautionSub procedures can be recursive, that is, they can call themselves to perform a given task. However, recursion can lead to stack overflow.

9. VBScript Procedures Function Procedures • To return a value from a function, assign the value to the function name. • If no value is assigned to name, the procedure returns a default value • a numeric function returns 0 • string function returns a zero-length string (""). • A function that returns an object reference returns Nothing if no object reference is assigned to name.

10. VBScript Procedures Function Procedures • Variables used in Function procedures fall into two categories: those that are explicitly declared within the procedure and those that are not. • Variables that are explicitly declared in a procedure (using Dim or the equivalent) are always local to the procedure. • Variables that are used but not explicitly declared in a procedure are also local unless they are explicitly declared at some higher level outside the procedure.

11. VBScript Procedures Function Procedures • CautionA procedure can use a variable that is not explicitly declared in the procedure, but a naming conflict can occur if anything you have defined at the script level has the same name. • If your procedure refers to an undeclared variable that has the same name as another procedure, constant, or variable, it is assumed that your procedure is referring to that script-level name. • To avoid this kind of conflict, use an Option Explicit statement to force explicit declaration of variables.

12. Function Procedures • CautionVBScript may rearrange arithmetic expressions to increase internal efficiency. • Avoid using a Function procedure in an arithmetic expression when the function changes the value of variables in the same expression.

13. Function Procedures • In the following example, the Celsius function calculates degrees Celsius from degrees Fahrenheit. • Sub ConvertTemp() • Dim Temp • temp = InputBox("Please enter the temperature in degrees F.", 1) • MsgBox "The temperature is " & Celsius(temp) & " degrees C." • End Sub • FunctionCelsius(fDegrees) • Celsius = (fDegrees - 32) * 5 / 9 • End Function

14. Getting Data into and out of Procedures • Each piece of data is passed into your procedures using an argument . • Arguments serve as placeholders for the data you want to pass into your procedure. • You can name your arguments any valid variable name. • When you create a procedure using either the Sub statement or the Function statement, parentheses must be included after the name of the procedure. • Any arguments are placed inside these parentheses, separated by commas. • To get data out of a procedure, you must use a Function. Remember, a Function procedure can return a value; a Sub procedure can't.

15. Sub Implementation • Getting an argument Sub doLoops (iNum)Dim iFor i = 1 To iNum Step 1‘ do nothingNextEndSub • Sending an argument doLoops 5 Call doLoops(5)

16. Sub Implementation • Getting several arguments Sub doLoops (iNum,strString)Dim iFor i = 1 To iNum Step 1‘ do nothingNextEndSub • Sending an argument doLoops 5,”Hello” Call doLoops(5,Hello)

17. Sub Implementation • Getting an argument Function ByteMe (sngNum) ByteMe = CByte(sngNum) EndFunction • Sending an argument X = ByteMe(5.5)

18. Sub Implementation • Getting several arguments Function ByteMe (sngNum,ByRef errNumber) ByteMe = CByte(sngNum) errNumber = Err.Number EndFunction • Sending an argument X = ByteMe(5.5,errNumber)

19. Call Statement • To call a Sub procedure from another procedure, type the name of the procedure along with values for any required arguments, each separated by a comma. • The Call statement is not required, but if you do use it, you must enclose any arguments in parentheses. • The Call statement Transfers control to a Sub or Function procedure. • If you omit the Call keyword, you also must omit the parentheses around argumentlist.

20. Call Statement • If you use either Call syntax to call any intrinsic or user-defined function, the function's return value is discarded. • Call MyFunction("Hello World") • Function MyFunction(text) • MsgBox text • End Function

21. Arguments ByVal and ByRef • ByVal| ByRef] varname • ByVal • Indicates that the argument is passed by value. • ByRef • Indicates that the argument is passed by reference.

22. Excercise

23. Lab 7.1 • Use the InputBox for retrieve two numbers,representing the flanks of a rectangle. • Write 2 functions : • First function calculates the area of the rectangle • Second function calculates the perimeter of the rectangle • The results must be displayed in a two lined msg box, each line for each result + information icon + EX 7.1 title.

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