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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

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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

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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

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Primary purposes of subs and functions
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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

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Sub Procedures (continued)
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Sub Procedures (continued)
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Gladis Antiques Application

• Manager wants an application to calculate
  employees 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

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Gladis Antiques Application (continued)
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Gladis Antiques Application (continued)
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Gladis Antiques Application (continued)
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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

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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

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Passing Variables by Value
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Passing Variables by Value (continued)
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Passing Variables by Reference
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Passing Variables by Reference (continued)
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Passing Variables by Reference (continued)
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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

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Function Procedures (continued)
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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

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The Pine Lodge Application (continued)
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The Pine Lodge Application (continued)
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The Pine Lodge Application (continued)
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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

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TOE Chart
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User Interface
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Objects, Properties, and Settings
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Tab Order
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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

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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

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Code
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Code (continued)
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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

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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