1. 3. User Defined Functions

2. Procedures and Functions
Both Procedures and Functions
Group of statements
Identified by unique name
mirror real life activities
Procedures – just do something
Functions – return a value

3. Built in Functions: SQR
Sqr – gives square a number
function Sqr(X: Extended): Extended;
Examples
Sqr(4) 16
Sqr(3) 9
Sqr(2) 4
X: Extended
Sqr
Extended

4. Built in Functions: Random
Random – generates random numbers
function Random(): Extended;
function Random(Limit: Integer): Integer;
Random
Extended
Limit: integer
Random
integer

5. User Defined Functions
Syntax very similar to procedure definition:
function <name>(<parameters>): <type>;
begin
...
Result := <value>
end;
Where
<name> represents function’s name you choose
<parameters> represent information needed
<type> represents the return type
<value> represent the return value

6. Exercise: code to diagram
Draw function diagram for the following code:
function Thing(): double;
function Miles(km: real): real;
function Double(num: integer): integer;

7. Exercise: diagram to code
Generate the code for the following diagrams:
Mins: integer
Minutes
integer
Hours: integer
Pounds: integer
Euros
integer

8. Example: Functions Demo (form)

9. Example: Functions Demo (code)
implementation
...
const MinutesPerHour = 60;
const KMperMile = 1.6;
function Minutes(Mins: integer; Hours: integer): integer;
begin
Result := Mins + (Hours * MinutesPerHour);
end;
function Miles(km: real): real;
Result := km / KMperMile;
procedure TfrmFuncts.cmdMinutesClick(Sender: TObject);
var tmpMins: integer;
var tmpHours: integer;
var resMins: integer;
tmpMins := StrToInt(txtMins.Text);
tmpHours := StrToInt(txtHours.Text);
resMins := Minutes(tmpMins, tmpHours);
lblMinutes.Caption := IntToStr(resMins);
procedure TfrmFuncts.cmdMilesClick(Sender: TObject);
var tmpKM: real;
var resMiles: real;
tmpKM := StrToFloat(txtKM.Text);
resMiles := Miles(tmpKM);
lblMiles.Caption := FloatToStr(resMiles);
end.

10. Meet George
Common Boa Constrictor (Boa Constrictor Constrictor).

11. George (cont.) Problem: Solution 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

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

13. George (cont.) The code: function FtoC(F: double): double; begin
end;