Chapter 5 - General Procedures

1. Chapter 5 - General Procedures 5.1 Function Procedures 5.2 Sub Procedures, Part I 5.3 Sub Procedures, Part II 5.4 Modular Design

2. Devices for Modularity Visual Basic has two strategies for breaking problems into smaller pieces: • Function procedures (Section 5.1) • Sub procedures (Section 5.2, 5.3)

3. 5.1 Function Procedures • User-Defined Functions • Having No Parameters • Having One Parameter • Having Multiple Parameters • Return • Any single value of any data type including Boolean

4. Some Built-In Functions Function: Int Example: Int(2.6) is 2 Input: double Output: integer Function: Math.Round Example: Math.Round(1.23, 1) is 1.2 Input: double, integer Output: double

5. Some Built-In Functions (continued) Function:FormatPercent Example: FormatPercent(0.12, 2) is 12.00% Input: double, integer Output: string Function: FormatNumber Example: FormatNumber(12.62, 1) is 12.6 Input: double, integer Output: string

6. Function Procedures • Function procedures (also called user-defined functions) always return one value • Syntax: FunctionFunctionName(ByValvar1 As Type1, ByValvar2 As Type2, ...) As ReturnDataType statement(s) Returnexpression End Function

7. Create a program that calls a function that converts a Fahrenheit temperature to Celsius. Example 1: Form txtTempF txtTempC

8. Creating a Function • Pick a name that describes the purpose of the function…FtoC in our case. • What is the input for this function? • Input(s) are the arguments or parameters in the function call • Temperature in Fahrenheit is the input • What is the output for the function? • This is the single value calculated and returned by the user-defined function. • Temperature in Celsius is the output

9. 3 Ways to Make aFunction Call • Just like calling: listbox1.items.add(Math.Sqrt(9)) textbox1.text = Math.Sqrt(9) answer = Math.Sqrt(9) • We will make a call to FtoC and pass the fahrenheit temperature: listbox1.items.add(FtoC(fahrenheitTemp)) textbox1.text = FtoC(fahrenheitTemp) celsius= FtoC(fahrenheitTemp)

10. Defining Function FtoC • Type “Function FtoC” in the Class • Type “(t As Double)” – this single parameter identifies the fahrenheit value being passed in. • Type “As Double” at the end -- tells the data type of the value to return – in this case a celsius value which is a double. Function FtoC(ByVal t AsDouble) AsDouble 'Convert Fahrenheit temp to Celsius Return (5 / 9) * (t - 32) EndFunction The value retuned must be the same data type as defined here!

11. Function Header Terminology

12. Example 1: Output

13. Example 1: The Complete Code Private Sub btnConvert_Click(...) _ Handles btnConvert.Click Dim fahrenheitTemp, celsiusTemp As Double fahrenheitTemp = CDbl(txtTempF.Text) celsiusTemp = FtoC(fahrenheitTemp) txtTempC.Text = CStr(celsiusTemp ) End Sub Function FtoC(ByVal t AsDouble) AsDouble Return (5 / 9) * (t - 32) EndFunction FtoC is called with 212° from txtTempF t is passed the value 212 Since (5/9)*(212-32) = 100, 100 is returned to the calling statement and assigned to celsiusTemp

14. Functions and Their Data Types Private Sub btnConvert_Click(...) Handles btnConvert.Click Dim fahrenheitTemp, celsiusTemp As Double fahrenheitTemp = CDbl(txtTempF.Text) celsiusTemp = FtoC(fahrenheitTemp) txtTempC.Text = CStr(celsiusTemp ) End Sub Function FtoC(ByVal t AsDouble) AsDouble Return(5 / 9) * (t - 32) EndFunction The data type of the return value must be the same as the data type at the end of function FtoCand the variable that is assigned a value from FtoC

15. Create a Function to return someone’s first name given their full name. Example 2: Form txtFullName txtFirstName

16. Defining the FirstName Function • Name the Function • FirstName • Argument to Parameter pass • fullName – someone’s full name (string) • Return Value • fristName – the person’s first name (string)

17. Creating the Calling Statement • The following statement calls the FirstNamefucntion with an agrument called fullName, calculates a value in the fucntion and assigns the return value to a textbox. txtFirstName.Text= FirstName(fullName)

18. Defining Function FirstName • Type “Function FirstName” in the Class • Type “(fullName As String)” – this single parameter identifies the full name being passed in. • Type “As String” at the end -- tells the data type of the value to return – in this case their first name. Function FirstName(ByVal fullName As String) As String 'Extract first name from full name Dim firstSpace As Integer firstSpace = fullName.IndexOf(" ") Return fullName.Substring(0, firstSpace) EndFunction

19. Example 2: Output

20. Example 2: The Completed Code Private Sub btnDetermine_Click(...) HandlesbtnDetermine.Click Dim fullName As String fullName = txtFullName.Text txtFirstName.Text = FirstName(fullName) End Sub Function FirstName(ByVal fullName As String)As String Dim firstSpace As Integer firstSpace = fullName.IndexOf(" ") ReturnfullName.Substring(0, firstSpace) End Function fullName is assigned“Franklin Delano Roosevelt” from txtFullName Franklin Delano Roosevelt is passed to fullName Franklin Since firstSpace = 8 and fullName.Substring(0,8) = “Franklin” is returned to the calling statement and assigned to txtFirstName

21. Create a Function to return someone’s earnings given their hourly wage and # of hours worked. Example 3: Passing Multiple Parameters txtWage txtHours txtEarnings

22. Defining the Earnings Function • Name the Function • Pay • Argument to Parameter pass • hourlyWage– dollars paid per hour (double) • hoursWorked – # of hours worked (double) • Return Value • Pay – dollars paid for the job (double)

23. Example 3: Partial Code Private Sub btnCalculate_Click(...) _ Handles btnCalculate.Click Dim hourlyWage, hoursWorkded As Double hourlyWage = CDbl(txtWage.Text) hoursWorked = CDbl(txtHours.Text) txtEarnings.Text = FormatCurrency(Pay(hourlyWage, hoursWorked)) End Sub Function call

24. User-Defined Pay Function With Multiple Parameters Function Pay(ByVal wage As Double, ByVal hrs As Double) As Double Dim amt AsDouble If hrs <= 40 then amt = wage * hrs Else amt = wage * 40 +(1.5 * wage * (hrs – 40)) End If Return amt End Function Function header The dimmed data type for amt must be the same as the data type at the end of the function header!

25. Example 3: Output

26. Example 3: The Complete Code Private Sub btnCalculate_Click(...) Handles btnCalculate.Click Dim hourlyWage, hoursWorkded As Double hourlyWage = CDbl(txtWage.Text) hoursWorked = CDbl(txtHours.Text) txtEarnings.Text = FormatCurrency(Pay(hourlyWage, hoursWorked)) End Sub Function Pay(ByVal wage As Double,ByVal hrs As Double) As Double Dim amt AsDouble 'amount of salary If hrs <= 40 then amt = wage * hrs Else amt = wage * 40 +(1.5 * wage * (hrs – 40)) End If Return amt End Function 14.50 45 14.50 45 Since hrs is > 40, amt = 14.50*40+(1.5*14.5*(45-40)) = 688.75 688.75

27. User-Defined Function Having No Parameters • Some functions like Math.Pi ( ) do not have parameters. • We will NOT create functions with inputs entered inside of the function. Function CostOfItem() As Double Dim price AsDouble = CDbl(txtPrice.Text) Dim quantity AsInteger = CDbl(txtQuantity.Text) Dim cost = price * quantity Returncost EndFunction

28. User-Defined Boolean-Valued Function Function IsVowelWord(ByVal word As String) As Boolean Dim found as Boolean = False If word.IndexOf("A") <> -1 Then found =True End If . . . If word.IndexOf("U") <> -1 Then found = True End If Returnfound End Function