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Objectives

1. 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. Procedure .

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Objectives

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  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 • 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 • 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 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

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