1. 1

2. Objectives
Explain the difference between a Sub procedure and a Function procedure
Create a Sub procedure
Create a procedure that receives information passed to it
Explain the difference between passing data by value and passing data by reference
Create a Function procedure
Microsoft Visual Basic .NET: Reloaded

3. Procedure
Procedure: a block of program code that performs a specific task
Function Procedure
Returns a value after performing its assigned task
Sub Procedure
Completes the task but does not return a value
Microsoft Visual Basic .NET: Reloaded

4. Sub Procedures Event procedure Independent Sub procedure
Associated with a specific object and event
Example: button click event
Independent Sub procedure
A collection of code that can be invoked from one or more places in an application
Processed only when called (invoked) from code
Invoke Sub using a Call statement from another procedure
Microsoft Visual Basic .NET: Reloaded

5. Sub Procedures (continued)
Private indicates procedure can only be used by other procedures in the current form
Sub keyword identifies procedure as a Sub Procedure
procedurename - name given to procedure
Naming rules same as for naming variables
parameterlist - optional set of memory locations referred to as parameters
ByVal, ByRef specify how parameter is passed
Microsoft Visual Basic .NET: Reloaded

6. Sub Procedures (continued)
Microsoft Visual Basic .NET: Reloaded

7. Sub Procedures (continued)
Microsoft Visual Basic .NET: Reloaded

8. Gladis Antiques Application
Manager wants an application to calculate employee’s regular pay, overtime pay, and gross pay
Employees are paid on hourly basis with time and one-half for overtime
Sub ClearLabels() will be used to clear display labels on form for 3 pay amounts
Microsoft Visual Basic .NET: Reloaded

9. Gladis Antiques Application (continued)
Microsoft Visual Basic .NET: Reloaded

10. Gladis Antiques Application (continued)
Microsoft Visual Basic .NET: Reloaded

11. Gladis Antiques Application (continued)
Microsoft Visual Basic .NET: Reloaded

12. Including Parameters in an Independent Sub Procedure
Call statement has an optional argumentlist
Comma separated list of arguments passed to procedure being called
Argumentlist must agree with number of parameters listed in parameterlist in the procedure header
Data type and position of each parameter must agree with data type and position of corresponding argument
Microsoft Visual Basic .NET: Reloaded

13. Passing Variables Pass by value Pass by reference Use keyword ByVal
Passes contents of variable to the parameter in receiving procedure but not memory location
Cannot change contents of passing variable
Pass by reference
Use keyword ByRef
Passes memory address of variable to the receiving procedure
Contents of variable can be changed within receiving procedure
Microsoft Visual Basic .NET: Reloaded

14. Passing Variables by Value
Microsoft Visual Basic .NET: Reloaded

15. Passing Variables by Value (continued)
Microsoft Visual Basic .NET: Reloaded

16. Passing Variables by Reference
Microsoft Visual Basic .NET: Reloaded

17. Passing Variables by Reference (continued)
Microsoft Visual Basic .NET: Reloaded

18. Passing Variables by Reference (continued)
Microsoft Visual Basic .NET: Reloaded

19. Function Procedures
Block of code that performs a task and returns a value after completing that task
Function header has keyword Function instead of Sub
Header has “As datatype” clause that specifies data type of value returned by the function
As Decimal - returns a decimal number
As String - returns a string
Return statement alerts computer that function has completed task and returns the value contained in its expression
Microsoft Visual Basic .NET: Reloaded

20. Function Procedures (continued)
Microsoft Visual Basic .NET: Reloaded

21. The Pine Lodge Application
Owner wants application to calculate new hourly pay given current pay rate and raise rate
Application demonstrates use of function procedure GetNewPay
Current pay rate and raise rate passed by value as parameters
New hourly pay returned by function
Microsoft Visual Basic .NET: Reloaded

22. The Pine Lodge Application (continued)
Microsoft Visual Basic .NET: Reloaded

23. The Pine Lodge Application (continued)
Microsoft Visual Basic .NET: Reloaded

24. The Pine Lodge Application (continued)
Microsoft Visual Basic .NET: Reloaded

25. Programming Example – Rainfall Application
Application allows user to enter monthly rainfall amounts for previous year
Calculates and displays the total rainfall amount and average rainfall amount
Microsoft Visual Basic .NET: Reloaded

26. TOE Chart
Microsoft Visual Basic .NET: Reloaded

27. User Interface
Microsoft Visual Basic .NET: Reloaded

28. Objects, Properties, and Settings
Microsoft Visual Basic .NET: Reloaded

29. Tab Order
Microsoft Visual Basic .NET: Reloaded

30. Pseudocode btnExit Click event procedure btnCalc Click event procedure
1. Close the application
btnCalc Click event procedure
1. call the CalctotalAndAverage procedure to calculate the total and average rainfall
2. display the total and average rainfall amounts in labels
Microsoft Visual Basic .NET: Reloaded

31. Pseudocode (continued)
CalcTotalAndAverage procedure
1. initialize the month counter to 1
2. repeat while amount is numeric
get a rainfall amount
if rainfall amount is numeric
add rainfall amount to total rainfall accumulator
add 1 to the month counter
else
display message informing user to enter a number
end if
end repeat
3. calculate the average rainfall = total rainfall / 12
Microsoft Visual Basic .NET: Reloaded

32. Code
Microsoft Visual Basic .NET: Reloaded

33. Code (continued)
Microsoft Visual Basic .NET: Reloaded

34. Summary
Procedures allow reuse of code throughout an application and allow programmer teamwork on large and complex applications
Function procedures return a value, Sub procedures do not
Independent Sub procedures and Functions are not associated with any specific object or event
Use Call statement to invoke an Independent sub procedure
Microsoft Visual Basic .NET: Reloaded

35. Summary (continued)
Number of arguments and data types must match in argumentlist and parameterlist
ByVal keyword passes contents of variable
Value of variable being passed cannot be changed in procedure
ByRef keywords passes the memory address
Value of variable being pass can be changed in procedure
Variables in parameterlist have procedure level scope
Microsoft Visual Basic .NET: Reloaded