Tutorials

1
Tutorials

• Do not just rely on the 6 lectures practice is
  vital.
• Labs every Monday 16.00-18.00 (A31).
• Tuesday 9.00-11.00 (A31).
• Dont leave everything to the last minute Come to
  the Labs.
• Pick up Pascal as soon as possible you will
  need to do some form of self-learning. On the HLL
  website there are links to
• - Borland on-line tutorials
• - the ICP module Web site
• - Object Pascal Language Guide.

2
Last Lecture

• Last Lecture we covered the following
• Why Delphi is Goodness
• Delphi IDE
• Object-oriented Pascal
• Pascal Units
• Variables
• Operators
• Strings
• Decisions Loops

3
This Lecture

• In Todays Lecture we will cover
• String Manipulation
• Mathematical Functions
• Records
• Functions and Procedures
• Pointers
• Dynamic Memory Allocation
• Classes
• That will be the end of Object Pascal.

4
1. Mathematical Functions

• Ln - Natural Logartihm
• Sqr - Square
• Sqrt - Square Root
• Pi - Pi
• Cos - Cosine
• Sin - Some
• Abs - Absolute Value
• Frac - Fractional Part of a Real
• Int - Integer part of a Real
• Round - Rounds a Real to an integer
• Trunc - Truncates a Real to an integer
• Random - Returns a random number

5
2. String and Character Functions

• In order that you can successfully manipulate
  strings for use in Delphi, you must be familiar
  with the various string and character function
  available in Object Pascal. In the following
  slides, I will cover some of these functions.
• Always remember that in Pascal a string is a
  character array starting from the 1 not 0
  element.
• Eg. If Str Jim then str1J, str2i,
  str3m

6
String and Character Functions

• Object Pascal provides string functions for
• - Concatenation
• - Case Conversion
• - Copying a Substring
• - Deleting a Substring
• - Inserting characters into a String
• - Searching for Characters in a string
• - Composite Operations (eg. Replace)

7
Chr

• Chr returns a character with a specified
  ordinal value.
• Chr(X Byte) Char.
• var i Integer
• begin
• for i 32 to 126 do
• write(Chr(i))
• end.

8
Concat

• Concat concatenates a character with a
  specified ordinal number.
• Concat(s1,s2,,sn String) String
• var s string
• begin
• sconcat(ABC,DEF)
• end.
• ABCDEF

9
Copy

• Copy returns a sub-string of a string.
• Copy(S String Index Integer Count Integer)
  String
• var s string
• begin
• s ABCDEF
• s copy(s, 2, 3)
• end.
• BCD

10
Delete

• Delete deletes a sub-string from a string.
• Delete(var SString Index Integer Count
  Integer)
• var s string
• begin
• s Big Tim Brailsford
• delete(s, 9, 10)
• label1.caption s
• end.
• Big Tim

11
Insert

• Insert inserts a sub-string into a string.
• Insert(Source String var S String
  IndexInteger)
• var s string
• begin
• s Little Hopkins
• insert(Kevin , s, 7)
• label1.caption s
• end.
• Little Kevin Hopkins

12
Length

• Length returns the dynamic length of a string.
• Length(S String) Integer
• var s string
• begin
• s Aston Villa
• lenlabel.caption length(s)
• end.

13
Pos

• Pos searches for a sub-string in a string.
• Pos(Substr String SString) Byte
• var s string
• begin
• s 123.5
• convert spaces to zeros
• while pos( , s) gt 0 do
• spos( , s) 0
• end.

14
Str IntToStr

• Str converts a numeric value to a string.
• Str(X Width Decimals var S String)
• var s string
• i integer
• begin
• I 123
• str(i, s)
• end.
• s contains 123

15
UpperCase LowerCase

• UpperCase converts a string to upper case
  letters.
• LowerCase converts a string to lower case
  letters.
• begin
• label1.caption UpperCase(Hello)
• end

16
StrPas StrPCopy

• The Delphi component classes use null-terminated
  strings. This can be confusing.
• To convert from a Delphi type string (PChar or
  array of Char) to a Pascal type string, use the
  StrPas function.
• To convert the other way, use the StrPCopy
  function.

17
Format

• Format formats and returns a string based on
  the format string and arguments passed, just like
  printf.
• E.g. the following adds two numbers, then uses
  Format to build a string to report the result
• var
• S String
• X Integer
• begin
• X 10 20
• S Format(The result is d, X)
• Label1.Caption S
• end

18
Format

• You could also do the calculation within the
  Format function.
• output 20 5 25
• var
• X Integer
• Y Integer
• begin
• X 20
• Y 5
• Label1.Caption
• Format (d d d, X, Y, X Y)
• end

19
3. Records

• A record is a collection of related data
  identified as a single storage unit, equivalent
  to a C struct.
• A record is declared as follows
• Type Person record
• FirstName string
• LastName string
• Address string
• Age Integer
• end

20
Records

• Each variable that you place in a record
  definition is called a field.
• Once a record has been defined, instances of that
  record can be created for use in your program.
• To create an instance of a record, define it as a
  new variable
• var
• MyRecord TPerson

21
Records

• You can now assign values to the fields
• MyRecord.FirstName James
• MyRecord.LastName Goulding
• MyRecord.Address Room C14
• MyRecord.Age 26
• The dot operator, or structure member selector,
  is placed after the record name and before the
  field name for that record.

22
4. Functions Procedures

• Functions and Procedures are key to procedural
  programming.
• Procedural programming improves efficiency and
  clarity by compartmentalising repetitive tasks.
• You can survive Delphi with just a knowledge of
  procedural programming. Delphi is OO, but the
  component classes are hidden from the user.

23
4. Functions

• The anatomy of a function in Pascal

24
Procedures

• A procedure is a section of code, similar to a
  function, except that it does not have a return
  value.
• The syntax is similar to a function except you
  use the procedure keyword and there is no return
  value type specified.
• procedure ChangeCaption(x string)
• var y string
• begin
• y The new caption is
• label1.caption x y
• end

25
Parameters

• You can pass variables into a function or
  procedure by value or by reference.
• When you pass a variable by value into a
  function, the variable passed in is only changed
  locally within the function.
• Passing by reference makes global changes to a
  variable passed in. To pass by reference, you
  should include a var keyword in front of any
  variables you wish to pass this way.

26
Passing by Value

• procedure cube(x integer)
• begin
• x xxx
• Label1.caption The answer is x
• end
• MAIN PROGRAM
  
• var number integer
• begin
• number 3
• cube(number)
• Label1.caption Label1.caption and
  number is number
• end
• Label 1 OUTPUT The answer is 27 and number
  is 3

27
Passing by Reference

• procedure cube(var x integer)
• begin
• x xxx
• Label1.caption The answer is x
• end
• MAIN PROGRAM
  
• var number integer
• begin
• number 3
• cube(number)
• Label1.caption Label1.caption and
  number is number
• end
• Label 1 OUTPUT The answer is 27 and number
  is 27

28
5. Pointers

• A pointer is a data type that contains a memory
  address of a variable.
• A pointer can point to a variable of any type
  (e.g. an integer, a string or a record).
• Pointers point to the address of the start of a
  data construct, so they are always the same size,
  regardless of what they are pointing to.

29
Pointer Syntax

• The Character byte is a pointer that is
  pointing to a byte
• var pt1 byte
• pt1 is the data pointed to by pt1
• writeln(pt1)
• The _at_ Character _at_myVar is the memory address
  of myVar
• var myVar byte
• pt1 byte
• ...
• pt1 _at_myVar
• writeln(pt1)

30
6. Dynamic Memory Allocation

• Memory Allocation normally automatically
  controlled. But you have to tell the computer how
  big a data sructure is. eg. Arrays
• The Heap is an area of memory that can be
  allocated while a program is running. (ie.
  Dynamically)
• Data allocated on the Heap occurs at a random
  address, and you cannot give the data a name.
• Hence we construct a pointer to tell us where
  our data is.

31
New and Dispose

• The new procedure allocates memory on the heap
  (dynamically allocatable memory).
• The dispose procedure de-allocates memory.
• var myString string
• begin
• new(myString)
• myString This is my string
• doSomething()
• dispose(myString)
• end

32
7. Classes

• A class is a collection of fields and methods
  (functions) that work together to accomplish a
  specific programming task.
• The function of a class is to encapsulate a task
  or concept. It contains all of the functions and
  variables relevant to that concept.
• Hence Classes have Properties (variables) and
  Capabilities (methods).
• You cannot write a complex program without
  classes. Do not be scared of them. They seem odd
  at first but quickly become second nature and
  speed up your programming.

33
Advantages of Classes

• Without classes Windows would not exist.
• Classes are Reusable.
• Libraries of reusable Classes (Class Libraries)
  make sophisticated functionality easily
  available.
• This is a construction kit approach to
  programming
• For example, consider graphical programs
• - Window Class
• - Text Box Class
• - Button Class
• - Label Class

34
A Class Example

• Consider a check-box Windows control component as
  an example.
• The class which represents a check-box would have
  fields for the caption of the check-box and for
  the state (checked or unchecked).
• There may be methods such as GetCheck, SetCheck,
  GetCaption and SetCaption.
• You can make separate instances (objects) of the
  class to control individual check-boxes.

35
Anatomy of a Class

• Classes have the following features
• Declaration
• Access Control
• Constructor
• Destructor
• Variables
• Methods
• A Special Pointer called self

36
Access Control

• A class, like a record, has a declaration. The
  class declaration is always in a type section.
• Classes have four levels of access
• Private
• Public
• Protected
• Published

37
Anatomy of a Class

• The public part of a class allows access to the
  outside world.
• The private part of a class is the internal
  implementation which is hidden from the outside
  world (data abstraction).
• The protected access level is similar to private,
  except its contents can be accessed by classes
  that are derived from the class.
• The published section publishes components.

38
Example Class Code

• Type
• Tvehicle class
• private
• Started Boolean
• Speed Integer
• procedure StartEngine()
• protected
• procedure StartUpProcedure()
• public
• HaveKey Boolean
• Start Boolean
• procedure Shutdown()
• end

39
The Constructor

• The constructor is a method that is used to
  create an instance of a class.
• If you dont provide a constructor, the base
  class constructor is called when you create the
  class (called Create).
• It must be declared using constructor keyword
• constructor Create constructor placed in
• public section

40
Instantiation of an Object

• An object is an instance of a class.
• Instantiation is the creation of an object.
• var MyCar Tvehicle
• begin
• MyCar Tvehicle.Create
• end

41
Destructors

• A destructor is a method which is automatically
  called before an object is destroyed.
• Type Example class
• private
• ...
• public
• constructor Create
• destructor Destroy
• end
• destructor Tvehicle.Destroy
• begin
• ...
• end

42
Methods

• Methods are functions or procedures that belong
  to a class.
• They are local to the class and can only be
  called from within a class itself or an instance
  of a class.
• Methods can be declared in the private,
  protected, or public sections of a class.

43
Delphi Classes and Objects

• The next few slides will cover the basics of
  classes and objects already in Delphi
• A set is a collection of values of one type.
• Consider the style property of a font object.
  This property can include one or more of the
  following values
• fsBold
• fsItalic
• fsUnderline
• fsStrikeOut

44
Using a Set

• Lets say you have an instance of the FontStyle
  object and you want to add bold and italic styles
  to the set of properties for that instance.
• This is how you would do it
• var
• Styles TFontStyles
• begin
• Styles Styles fsBold, fsItalic
• Memo.Font.Style Styles
• end

45
Labs

• First Labs occur on Monday after the FAI lecture.
• There will be a new example sheet in each Lab.
• We will generally only cover simple things Hello
  World program, basic event handling, label
  displaying and file input/output.
• It is up to you to put in time with the on-line
  tutorials and try to learn some features for
  yourself )