6c – Function Procedures

1. 6c – Function Procedures CSCI N331 VB .NET Programming Lingma Acheson Department of Computer and Information Science, IUPUI

2. 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)

3. Procedures 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 label End 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 out End of Add procedure Sub 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 label End of Add procedure

4. 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

5. 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(ByValintOne As Integer, ByValintTwo As Integer) As Integer Dim intResult As Integer = 0 intResult= intOne + intTwo Return intResult ‘pass the result out ‘intResult is unnecessary. The above three lines can be replaced by the ‘following line ‘Return (intOne + intTwo) End Function

6. 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 Boolean If (intScore >=60) Then blnPass = True Else blnPass = False