Add first class examples

simple_examples/class_intro.pas

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+program class_intro;
+
+{$mode objfpc}{$H+}
+
+type TGrandParent = class(TObject)
+	procedure WriteAboutMyself;
+end;
+
+procedure TGrandParent.WriteAboutMyself;
+begin
+	WriteLn();
+	WriteLn('The name of this class is ', self.ClassName);
+	WriteLn('  its parent is ', self.ClassParent.ClassName);
+	WriteLn('    its InstanceSize is ', self.InstanceSize);
+	WriteLn('      its declaration is located in ', Self.UnitName);
+end;
+
+type
+	TParent = class(TGrandParent)
+		FintField: integer;
+	end;
+
+	TChild = class(TParent)
+		FsetField: set of byte;
+	end;
+
+var exampleClass: TGrandParent;
+begin
+	exampleClass := TGrandParent.Create;
+	exampleClass.WriteAboutMyself;
+	exampleClass.Free;
+
+	exampleClass := TParent.Create;
+	exampleClass.WriteAboutMyself;
+	exampleClass.Free;
+
+	exampleClass := TChild.Create;
+	exampleClass.WriteAboutMyself;
+	exampleClass.Free;
+
+	{$IFDEF WINDOWS}
+	ReadLn;
+	{$ENDIF}
+end.

simple_examples/person_class.pas

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+program person_class;
+
+{$mode objfpc}{$H+}
+
+uses sysutils, dateutils;
+
+type
+	TPerson = class
+		FAwards: array of string;
+		FBirth, FDeath: TDate;
+		FName, FNationality, FRole: string;
+
+		constructor Create(aName, aNationality, aRole, aBirth, aDeath: string);
+		destructor Destroy; override;
+		function GetAwards(index: integer): string;
+		function GetLifespan: integer;
+		function GetNumberOfAwards: integer;
+		procedure DisplayInfo;
+		procedure SetAwards(index: integer; AValue: string);
+
+		property Awards[index: integer]: string read GetAwards write SetAwards;
+		property Birth: TDate read FBirth;
+		property Death: TDate read FDeath;
+		property Lifespan: integer read GetLifespan;
+		property Name: string read FName;
+		property NumberOfAwards: integer read GetNumberOfAwards;
+		property Role: string read FRole;
+	end;
+
+function TPerson.GetAwards(index: integer): string;
+begin
+	if Length(FAwards) > index
+		then Result := FAwards[index]
+	else Result := EmptyStr;
+end;
+
+function TPerson.GetNumberOfAwards: integer;
+begin
+	Result := Length(FAwards);
+end;
+
+procedure TPerson.SetAwards(index: integer; AValue: string);
+begin
+	SetLength(FAwards, index+1);
+	FAwards[index] := AValue;
+end;
+
+function TPerson.GetLifespan: integer;
+begin
+	if FDeath = 0 then Result := YearsBetween(Now, FBirth)
+	else Result := YearsBetween(FDeath, FBirth);
+end;
+
+constructor TPerson.Create(aName, aNationality, aRole, aBirth, aDeath: string);
+begin
+	inherited Create;
+	FName := aName;
+	FNationality := aNationality;
+	FRole := aRole;
+	FBirth := StrToDate(aBirth);
+
+	if (aDeath = EmptyStr) then FDeath := 0
+	else FDeath := StrToDate(aDeath);
+end;
+
+destructor TPerson.Destroy;
+begin
+	SetLength(FAwards, 0);
+	inherited Destroy;
+end;
+
+procedure TPerson.DisplayInfo;
+var n: integer;
+begin
+	WriteLn('The ', FNationality, ' ', FRole, ' ', Name, ' was born on ', DateToStr(Birth));
+
+	case FDeath = 0 of
+		True: WriteLn(' is alive today and is ', Lifespan, ' years old');
+		False: WriteLn(' and died on ', DateToStr(Death), ' aged ', Lifespan, ' years');
+	end;
+
+	if NumberOfAwards > 0
+		then for n := Low(FAwards) to High(FAwards)
+			do WriteLn('    achieved in ', Awards[n]);
+
+	WriteLn;
+end;
+
+var person: TPerson;
+begin
+	person := TPerson.Create(
+		'John Lennon',
+		'British',
+		'songwriter',
+		'09-10-1940',
+		'08-12-1980'
+	);
+	person.DisplayInfo;
+	person.Free;
+
+	person := TPerson.Create(
+		'Arvo Part',
+		'Estonian',
+		'composer',
+		'11-08-1935',
+		''
+	);
+	person.displayInfo;
+	person.Free;
+
+	person := TPerson.Create(
+		'Usain Bolt',
+		'Jamaican',
+		'sprinter',
+		'21-08-1986',
+		''
+	);
+	person.Awards[0] := 'Berlin 2009 100m world record of 9.58s';
+	person.Awards[1] := 'Berlin 2009 200m world record of 19.19s';
+	person.Awards[2] := 'London 2012 100m Olympic record of 9.69s';
+	person.Awards[3] := 'London 2012 200m Olympic record of 19.30s';
+	person.DisplayInfo;
+	person.Free;
+
+	{$IFDEF WINDOWS}
+	ReadLn;
+	{$ENDIF}
+end.