6c – Function Procedures

Lingma AchesonDepartment of Computer and Information Science, IUPUI

CSCI N331 VB .NET Programming

Function Procedures• Sometimes a procedure produces a

result, e.g. – CStr(intResult) will change the type of the

intResult value from an Integer type to a String type. The result is the value in the String format.

– Add(1, 2) will produce an addition result of 3.

• A procedure that generates a result is called a Function Procedure. A procedure that doesn’t generate a result is called a Sub Procedure.

• We can give the result to another variable.E.g.intResult = Add(intInput1, intInput2)

lblResult.Text = CStr(intResult)

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ProceduresSub Procedures:Button click event procedure: Create variables 1, 2 Take the user input and store in variable 1 and 2 ‘Tell the procedure what to add Add(variable1 and variable2)End of event procedure

Procedure Add(variable1 and variable2): Create variable 3 Add variable 1 to variable 2 and store in variable 3 display result in labelEnd of Add procedure

Can be changed to:Button click event procedure: Create variables 1, 2 Create variable 3 Take the user input and store in variable 1 and 2 variable 3 = Add(variable1 and variable 2) ‘use the result in this procedure display variable 3 in labelEnd of event procedure

Procedure Add(variable1 and variable2) Create variable 4 Add variable 1 to variable 2 and store in variable 4 pass the value of variable 4 outEnd of Add procedure

Function Procedures• Function - A type of procedure that produces a

result– Example:

Function procedure call and use the result:

dblResult = Add(dblInput1, dblInput2)

Function procedure definition: ‘”As Double” indicates that the function produces a

double value

Private Function Add(ByVal dblValue1 As Double, ByVal

dblValue2 As Double) As Double

Dim dblValue3 As Double

dblValue3 = dblValue1 + dblValue2

Return dblValue3

End Function– Return xxx: when the Function finishes execution, xxx is the

value to be passed out. Can be a value or a variable name.– Functions can also take parameters, just like Subs

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Function Procedures– E.g.

Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisplay.Click

…‘Function Add takes two parameters, does the addition and

passes the ‘result out to the intAddResult.

intAddResult = Add(intFirst, intSecond) ‘Function call

txtAddResult.Text = CStr(intAddResult) End Sub

‘Function takes two integer parameters and returns an integer as the result

Private Function Add(ByVal intOne As Integer, ByVal intTwo As Integer) As Integer

Dim intResult As Integer = 0intResult= intOne + intTwoReturn intResult ‘pass the result out‘intResult is unnecessary. The above three lines can be

replaced by the ‘following line‘Return (intOne + intTwo)

End Function

Function Procedures– Each function can only return one value. E.g, In the following code, although there are two return

statements, only one return statement will be executed.

If (a condition is true) Then

return True ‘return a boolean value

Else

return False

End If

– Boolean data type revisit –

A boolean variable only has two values, True or False. It is often used to indicate a situation is true or false. E.g.

Dim blnPass As BooleanIf (intScore >=60) Then

blnPass = TrueElse blnPass = False