10 – User Defined Functions

1. 10 – User Defined Functions

2. Session Aims & Objectives • Aims • To introduce user defined functions • Objectives,by end of this week’s sessions, you should be able to: • Create your own function definitions • Call these functions

3. Procedures and Functions • Both Procedures and Functions • Group of statements • Identified by uniquename • mirror real life activities • Procedures – just do something • Functions – return a value

4. Built in Functions: Sqr X: Double Sqr Double • Sqr – gives square root of a number: • Examples Sqr(4) returns 16 Sqr(3) returns 9 Sqr(2) returns 4 Option Explicit Private Sub txtNum_Change() Dim tmpNum As Double tmpNum = Val(Me.txtNum.Text) Me.lblResult.Caption = Sqr(tmpNum) End Sub SquareRoot

5. Built in Functions: Rnd Random Single • Rnd() function • generates pseudo-random numbers • >= 0 and <1 • Randomize – initialises random number generator RandomNumbers Option Explicit Private Sub Form_Load() Randomize End Sub Private Sub btnRandom_Click() Me.lblNum.Caption = Rnd() End Sub

6. User Defined Functions (how) • Syntax very similar to procedure definition: Function<name>(<parameters>) As <type> [<Statement-Block>] <name> = <value> End Function • Where • <name> represents function’s name you choose • <parameters> represent information needed • <type> represents the return type • <value> represent the return value

7. Exercise 1: Function Diagrams Thing double km: double Miles double num: long Twice long • Draw function diagram for the following code: Function Thing() As Double Function Miles(km As Double) As Double Function Twice(num As Long) As Long

8. Exercise 2: Function Headers Mins: integer Minutes integer Hours: integer Pounds: integer Euros integer • Generate the code for the following diagrams: Function Euros(Pounds As Integer) As Integer Function Minutes(Mins As Integer, _ Hours As Integer) As Integer

9. Function Implementation: Code • Function Header – gives: • name (e.g. Double), • parameter names and types (e.g. num: integer), and • return type (e.g. integer) • Function Body – gives code: Function Double(num As integer) As integer Double = num * 2 End Function num: integer Double integer

10. Meet George • Common Boa Constrictor • boa constrictor imperator • Native to Central & South America • No venom (no poison)

11. Meet George (cont.)

12. George (cont.) • Problem: • Difficult to keep • Require temperature and humidity controlled environment • Much of the literature is from the US • Temperature in Fahrenheit • Solution • Need a program to convert from Celsius to Fahrenheit

13. George (cont.) • To convert from Fahrenheit to Celsius: • To convert from Celsius to Fahrenheit:

14. Example 1: Temp v1 Temp v1 Option Explicit Private Sub Form_Load() lblResult.Caption = ((txtFah.Text - 32) * 5) / 9 End Sub Private Sub txtFah_Change() lblResult.Caption = ((txtFah.Text - 32) * 5) / 9 End Sub

15. FtoC Function • The declaration: Function FtoC(F As double) As double FtoC = ((f-32) * 5) / 9 End Function • The call: lblResult.Caption = FtoC(50)

16. Example 2: Temp v2 Temp v2 Option Explicit Function FtoC(F As Double) As Double FtoC = ((F - 32) * 5) / 9 End Function Private Sub Form_Load() lblResult.Caption = FtoC(txtFah.Text) End Sub Private Sub txtFah_Change() lblResult.Caption = FtoC(txtFah.Text) End Sub

17. Example 3: Total Total