Comprehensive Delphi Delphi Cram Notes and Study Notes Guide

Component Basics and Properties

Edit Box (.Text)
- What it does: Extracts or sets the text displayed in the Edit Box.
- Extract Example: sName := edtName.Text;
- Set Example: edtName.Text := sName; or edtName.Text := ‘Angela’;
Combo Box (.Text)
- What it does: Extracts or sets the text displayed in the Combo Box.
- Extract Example: sData := cmbData.Text;
- Set Example: cmbData.Text := sName; or cmbData.Text := ‘Adhi’;
ComboBox (.ItemIndex)
- What it does: Returns the index of the user’s selection from the ComboBox. The index starts at $0$ .
- Extract Example: iSel := cmbData.ItemIndex;
- Set Example: cmbData.ItemIndex := 0; (This sets the selection to the first item).
Radio Group (.Items)
- What it does: Extracts or adds option/option text to the Radio Group.
- Extract Example: sSel := rgpData.Items[rgpItems.ItemIndex]; or sSel := rgpData.Items[0];
- Set Example: rgpData.Items.Add(‘Coffee’);
Radio Group (.ItemIndex)
- What it does: Returns the index of the user’s selection from the Radio Group. The index starts at $0$ .
- Extract Example: iSel := rgpData.ItemIndex;
- Set Example: rgpData.ItemIndex := 0; (This sets the selection to the first item).
List Box (.Items)
- What it does: Extracts or adds option/option text to the List Box.
- Extract Example: sSel := lstData.Items[lstData.ItemIndex]; or sSel := lstData.Items[0];
- Set Example: lstData.Items.Add(‘Hot Chocolate’);
List Box (.ItemIndex)
- What it does: Returns the index of the user’s selection from the List Box. The index starts at $0$ .
- Extract Example: iSel := lstData.ItemIndex;
- Set Example: lstData.ItemIndex := 0; (This sets the selection to the first item).
Checkbox (.Checked)
- What it does: Returns a Boolean value where TRUE means the box is checked and FALSE means it is not checked.
- Extract Example: bMarried := chbMarried.Checked;
- Set Example: chbMarried.Checked := TRUE; (This ticks the box).
Label (.Caption)
- What it does: Extracts or sets the text displayed on the label.
- Extract Example: sText := lblHeading.Caption;
- Set Example: lblHeading.Caption := ‘Hello’; or lblHeading.Caption := sText;
Panel (.Caption)
- What it does: Extracts or sets the text displayed on the panel.
- Extract Example: sText := pnlWelcome.Caption;
- Set Example: pnlWelcome.Caption := ‘Hello’; or pnlWelcome.Caption := sText;
Rich Edit Box (.Text)
- What it does: Extracts, clears, and displays text.
- Extract Example: sLine := redOut.Text;
- Set Example: redOut.Text := ‘Hello’ + #9 + sName + #13 + ‘How are you?’;
- Constants used: #9 represents a tabspace; #13 represents a new line.
Rich Edit Box (.Lines.Add)
- What it does: Adds a new line and displays provided text.
- Set Example: redOut.Lines.Add(‘Hello’);
Rich Edit Box (.SelText)
- What it does: Adds data to the existing current line in the Rich Edit Box without moving to a new line.
- Set Example: redOut.SelText := ‘Hello’ + #9 + sName;
SpinEdit (.Value)
- What it does: Sets or returns the selected or typed numerical value.
- Extract Example: iAge := sedAge.Value;
- Set Example: sedAge.Value := 16;
DateTimePicker (.Date)
- What it does: Returns or sets the selected date.
- Extract Example: dtDate := dtPurchase.Date;
- Set Example: dtPurchase.Date := StrToDate(‘08/10/2018’);
DateTimePicker (.Time)
- What it does: Returns or sets the selected time.
- Extract Example: dtTime := dtPurchase.Time;
- Set Example: dtPurchase.Time := StrToTime(’16:49:20’);
ImageBox (.Picture)
- What it does: Displays a picture based on a specified filename.
- Action Example: imgProd.Picture.LoadFromFile(‘RedBull.jpg’);
MemoBox (.Text / .Lines)
- Details: Uses the same structure and methods (e.g., .Text, .Lines.Add) as the Rich Edit Box.

Pre-defined Math Class Methods

Round
- Action: Rounds a real number to the nearest whole number.
- Return Type: Integer.
- Example: rValue := 5 / 2; iValue := Round(rValue); (Results in iValue = 3).
Frac
- Action: Returns the fractional (decimal) part of a number.
- Return Type: Real.
- Example: rValue := 10 / 3; rNew := Frac(rValue); (Results in rNew = 0.3333).
Ceil
- Action: Rounds a fractional value up to the next integer.
- Return Type: Integer.
- Example: rValue := 10 / 3; rNew := Ceil(rValue); (Results in rNew = 4).
Floor
- Action: Rounds a fractional value down to the nearest integer.
- Return Type: Integer.
- Example: rValue := 5 / 3; rNew := Floor(rValue); (Results in rNew = 1).
FormatFloat
- Action: Converts a Real value to a formatted String.
- Return Type: String.
- Example 1: sOutput := FormatFloat(‘0.0’, 5.253); (Results in sOutput = 5.3).
- Example 2: sOutput := FormatFloat(‘R0.00’, 5.253); (Results in sOutput = R5.25).
Trunc
- Action: Removes the decimal part of a Real number (truncates).
- Return Type: Integer/Real.
- Example: rValue := 3.55; rNew := trunc(rValue); (Results in rNew = 3).
Power
- Action: Raises a base value to a specific exponent value.
- Return Type: Real.
- Example: rPow := power(5, 3); (Results in rPow = 125).
Sqrt
- Action: Calculates the square root of a provided value.
- Return Type: Real.
- Example: rSR := sqrt(64); (Results in rSR = 8).
Max
- Action: Returns the higher value between two provided numbers.
- Return Type: Integer/Real.
- Example: iBig := max(50, 20); (Results in iBig = 50).
Min
- Action: Returns the smaller value between two provided numbers.
- Return Type: Integer/Real.
- Example: iSmall := min(50, 20); (Results in iSmall = 20).
Abs
- Action: Returns the absolute value (positive distance from zero) of a number.
- Return Type: Integer/Real.
- Example: rNum := 30 - 50; rNum := abs(rNum); (Results in rNum = 20).
Pi
- Action: Returns the constant value of $\pi$ .
- Return Type: Real.
- Example: rCircleArea := pi * power(rRadius, 2);
Val
- Action: Attempts to convert a String to a Real number. If successful, returns an error code of $0$ . If unsuccessful, returns the index position of the error.
- Return Type: Integer (for Error Code), Real (for converted value).
- Example 1: val(‘500’, rNum, iError); (Results in rNum = 500, iError = 0).
- Example 2: val(‘5A5’, rNum, iError); (Results in rNum = undefined, iError = 2).
Succ
- Action: Returns the successor (next value) of the provided integer or character.
- Return Type: Integer/Char.
- Example: iNum := 50; iNum := succ(iNum); (Results in iNum = 51).
Pred
- Action: Returns the predecessor (previous value) of the provided value.
- Return Type: Integer/Char.
- Example: iNum := 49; iNum := pred(iNum); (Results in iNum = 48 - corrected from transcript typo which listed 49/49 outcomes).
RandomRange
- Action: Returns a random integer between a minimum and a maximum minus 1 ( $\text{min}$ to $\text{max} - 1$ ).
- Return Type: Integer.
- Example: iRan := RandomRange(50, 100); (Range: $50-99$ ).
Random
- Action: Returns a random integer from $0$ up to the specified value minus 1.
- Return Type: Integer.
- Example: iRan := Random(100); (Range: $0-99$ ).
Sign
- Action: Returns an integer indicating the sign of the number ( $-1$ for negative, $0$ for zero, $1$ for positive).
- Example: iSign := Sign(-205); (Results in iSign = -1).
CompareValue
- Action: Compares two values and returns $1$ if the first is greater, $-1$ if smaller, or $0$ if equal.
- Example: iCom := CompareValue(150, 100); (Results in iCom = 1).

Annexure B: Components, Events, and Methods Matrix

Key Components and Grades (10, 11, 12):
- Grade 10: TForm, TButton, TBitButton, TLabel, TEdit, TImage, TShape, TPanel, TListBox, TRadioGroup, TComboBox, TMemo, TRadioButton, TCheckBox.
- Grade 11: TSpinEdit, TTimer, TStringGrid, TDBGrid.
- Grade 12: TPageControl, TADOTable, TADOQuery, TDataSource.
General Methods:
- Show(), Hide(), SetFocus().
- Grade 11 Addition: setLength.
Conversion and Formatting:
- IntToStr(), StrToInt(), FloatToStr(), StrToFloat(), FloatToStrF() (Grade 11).
- Date/Time: FormatDateTime(), TimeToStr(), DateToStr(), DateTimeToStr(), StrToDate(), StrToTime().
Mathematical Methods:
- Random(), RandomRange(), Round(), Trunc(), Frac(), Ceil() (Grade 11), Floor() (Grade 11), Sqr(), Sqrt(), Pi (Grade 11), Power() (Grade 11).
- Inc(), Dec() (Grade 10).
String Handling:
- Length(), Pos(), Copy(), Insert(), Delete(), Concat(), UpCase(), UpperCase(), LowerCase(), IgnoreCase() (Grade 11).
- Ord(), Chr(), Val(), Str.
File Handling:
- AssignFile(), Append(), Reset(), Rewrite(), CloseFile(), FileExists(), Readln(), Writeln(), LoadFromFile(), SaveToFile().
UI and Messages:
- InputBox(), ShowMessage(), MessageDlg() (Grade 11).
Event Handlers:
- OnClick, OnCreate, OnActivate, OnShow, OnClose, OnTimer.

Database Code Constructs

General Reading Structure:

  tblExample.First;
  while not tblExample.EOF do
  Begin
    // Process Record
    tblExample.Next;
  End;
&nbsp;&nbsp;```

- **Calculating Sum and Average:**

pascal tblExample.First; rSum := 0; while not tblExample.EOF do Begin rSum := rSum + tblExample[‘Age’]; tblExample.Next; End; rAve := rSum / tblExample.RecordCount; ```

Finding Highest Value:

  tblExample.First;
  iHigh := tblExample[‘Age’];
  while not tblExample.EOF do
  begin
    if tblExample[‘Age’] > iHigh then
    begin
       iHigh := tblExample[‘Age’];
    end;
    tblExample.Next;
  end;
  // Note: Swap the > to < in the IF statement to find the Lowest value.
&nbsp;&nbsp;```

- **Updating the Current Record:**

pascal tblExample.Edit; tblExample[‘Name’] := ‘Erica’; tblExample[‘Age’] := 17; tblExample.Post; tblExample.Refresh; ```

Adding a New Record:

  tblExample.Append;
  tblExample[‘ID’] := IntToStr(tblExample.RecordCount + 1);
  tblExample[‘Name’] := ‘Ndumiso’;
  tblExample[‘Age’] := 17;
  tblExample.Post;
  tblExample.Refresh;
&nbsp;&nbsp;```

- **Deleting current Record:**
  - Use `tblExample.Delete;`. 
  - Important: In practical applications, always use a confirmation dialog box before finalizing a delete.

- **Locating a Specific Record:**

pascal sName := edtName.Text; bFound := FALSE; tblExample.First; while not tblExample.EOF do Begin If tblExample[‘Name’] = sName then Begin bFound := TRUE; End; tblExample.Next; End; ```

Block Adjustment (e.g., Update all ages):

  tblExample.First;
  while not tblExample.EOF do
  Begin
    tblExample.Edit;
    tblExample[‘Age’] := tblExample[‘Age’] + 1;
    tblExample.Post;
    tblExample.Refresh;
    tblExample.Next;
  End;
&nbsp;&nbsp;```

- **Counting (e.g., records with mark < 30):**

pascal iCount := 0; tblExample.First; while not tblExample.EOF do Begin If tblExample[‘Mark’] < 30 then Begin Inc(iCount); End; tblExample.Next; End; ```

Working with Two Tables (Parent and Child):

  tblParent.First;
  while not tblParent.EOF do
  Begin
    // obtain a pk field
    tblChild.First;
    while not tblChild.EOF do
    Begin
      If tblParent[‘PK’] = tblChild[‘FK’] then
      Begin
        // Action logic
      End;
      TblChild.Next;
    End;
    tblParent.Next;
  End;
&nbsp;&nbsp;```

- **Sorting Records:**
  - Syntax: `Tblname.sort := ‘Field ASC’;` (for ascending) or `Tblname.sort := ‘Field DESC’;` (for descending).

# Data Validation Examples

- **Text Only (A-Z, a-z):**

pascal bValid := TRUE; for i := 1 to Length(sWord) do Begin If not(sWord[i] in [‘A’..’Z’, ‘a’..’z’]) then Begin bValid := FALSE; End; End; ```

Text with Spaces and Length Check:

  bValid := TRUE;
  for i := 1 to Length(sWord) do
  Begin
    If not(sWord[i] in [‘A’..’Z’, ‘a’..’z’, ‘ ’]) then
      bValid := FALSE;
  End;
  If (Length(sWord) = 13) AND (bValid) then // Condition met
&nbsp;&nbsp;```

- **Digits Only (0-9):**

pascal bValid := TRUE; for i := 1 to Length(sWord) do Begin If not(sWord[i] in [‘0’..’9’]) then bValid := FALSE; End; ```

Text File Handling

Checking File Existence:
- Exist check: If FileExists(‘data.txt’) then...
- Non-existence check: If not FileExists(‘data.txt’) then...
Reading from a Text File:

  AssignFile(tFile, ‘data.txt’);
  Reset(tFile);
  While not eof(tFile) do
  Begin
    ReadLn(tFile, sLine);
  End;
  CloseFile(tFile);
&nbsp;&nbsp;```

- **Creating and Writing to a New Text File:**

pascal AssignFile(tFile, ‘new.txt’); Rewrite(tFile); WriteLn(tFile, sLine); CloseFile(tFile); ```

Appending to an Existing Text File:

  AssignFile(tFile, ‘myfile.txt’);
  Append(tFile);
  WriteLn(tFile, sLine);
  CloseFile(tFile);
&nbsp;&nbsp;```

# One-Dimensional Arrays

- **Declaration:** `arrNum : Array[1..5] of Integer;` 
- **Declaration with Initial Values:** `arrNum : Array[1..5] of Integer = (10, 50, 40, 100, 80);` 

- **Populating with Random Values (Range  $1-100$ ):**

pascal For i := 1 to 5 do arrNum[i] := RandomRange(1, 101); ```

Populating with User Input:

  For i := 1 to 5 do
    arrNum[i] := StrToInt(InputBox(‘Cram’, ‘Enter number’, ‘’));
&nbsp;&nbsp;```

- **Displaying Values:**
  - **Vertically (RichEdit):** `redOut.Lines.Add(IntToStr(arrNum[i]));` 
  - **Horizontally (EditBox):** `edtOut.SelText := IntToStr(arrNum[i]) + #9;` (using tabspace).

- **Sum and Average:**

pascal rSum := 0; For i := 1 to 5 do rSum := rSum + arrNum[i]; rAve := rSum / Length(arrNum); ```

Finding Highest in Parallel Arrays:

  iHigh := arrNum[1];
  sName := arrNames[1];
  for i := 2 to 5 do
  begin
    if arrNum[i] > iHigh then
    begin
      iHigh := arrNum[i];
      sName := arrNames[i];
    end;
  end;
&nbsp;&nbsp;```

- **Bubble Sort (Parallel Array Example):**

pascal iEndCounter := Length(arrTitle) - 1; repeat bSwapped := false; for k := 1 to iEndCounter do begin if arrTitle[k] > arrTitle[k + 1] then begin sKeep := arrTitle[k]; arrTitle[k] := arrTitle[k + 1]; arrTitle[k + 1] := sKeep; bSwapped := true; end; end; until (bSwapped = false); // For descending order, change the > to <. ```

Searching and Array Manipulation:
- Search: If iPos remains $0$ after a loop through the array, the item was not found.
- Delete: Move items from iPos upward to iMax - 1 and decrement the size counter (dec(iMax)). pascal for i := iPos to iMax - 1 do arrNum[i] := arrNum[i + 1]; dec(iMax);

Two-Dimensional Arrays

Declaration: arrNum : Array[1..5, 1..4] of Integer; (5 Rows, 4 Columns). Always reference Row ( $r$ ) first, then Column ( $c$ ).
Displaying in a StringGrid:
- Note: In a StringGrid, Column comes before Row: StringGrid1.Cells[c, r].
- Column/Row $0$ usually contains headings.
Transposing:
- Converting Rows to Columns: arrNew[r][c] := arrNum[c][r];. Ensure the new array has swapped row/column dimensions.
Diagonal Calculations (Square Arrays Only):
- Left Diagonal (): Loop iSum := iSum + arrNum[r][r]; from $1$ to $n$ .
- Right Diagonal (/): Start c at the max column and decrement while looping rows: iSum := iSum + arrNum[r][c]; dec(c);.
Swapping Logic:
- Swap Rows: Use a loop for columns and a temp variable: iTemp := arrNum[r1][c]; arrNum[r1][c] := arrNum[r2][c]; arrNum[r2][c] := iTemp;.
- Swap Columns: Use a loop for rows: iTemp := arrNum[r][c1]; arrNum[r][c1] := arrNum[r][c2]; arrNum[r][c2] := iTemp;.

Object-Oriented Programming (OOP)

Constructor:
- Declaration: Constructor CREATE(sName : String; sID : String);
- Implementation: Used to initialize private attributes (e.g., fName := sName;).
Accessor (Getter):
- A function returning an attribute value. Example: Function TClass.getAge : Integer; Begin Result := fAge; End;.
Mutator (Setter):
- A procedure to change an attribute. Example: Procedure TClass.setAge(iAge : Integer); Begin fAge := iAge; End;.
toString:
- A function returning a user-friendly string of attributes: Result := ‘Key: ’ + #9 + fName;.
Instantiation:
- Syntax: objLearner := TLearner.Create(sName, sID);.

String Handling Methods and Properties

Indexing: sSent[i] refers to a single character (type Char).
Set Inclusion: If sSent[i] in [‘a’, ‘e’, ‘i’, ‘o’, ‘u’] then...
Key Procedures:
- Insert(sSub, sLine, iPos): Adds a string into another at a position.
- Delete(sLine, iStart, iNumChars): Removes characters from a string.
Key Functions:
- Length(sString): Returns integer length.
- Pos(sSub, sMain): Returns integer starting position of a substring.
- Copy(sString, iStart, iLen): Returns a substring.
- Uppercase(sString) / Upcase(Char): Converts to capitals.

Time, Date, and Pop-up Dialogs

Functions:
- Now(): Current date and time.
- Date(): Current system date.
- Time(): Current system time.
- IsLeapYear(Year): Returns Boolean TRUE if leap year.
- YearOf(dDate), MonthOf(dDate), DayOf(dDate): Extract components as integers.
MessageDlg:
- Syntax: If MessageDLG(‘Exit?’, mtWarning, [mbOK, mbCancel], 0) = mrOK then...
- Types: mtWarning, mtConfirmation, mtInformation, mtError, mtCustom.
- Buttons: mbYes, mbNo, mbOK, mbCancel, mbAbort, mbRetry, mbIgnore, mbAll.
- Return values: mrYes, mrNo, mrOK, mrCancel, etc.

Mathematical Functions Summary

Sqr(num): Returns the square ( $x^2$ ). Example: sqr(-5) = 25.
Sqrt(num): Returns the square root ( $\sqrt{x}$ ). Example: sqrt(9) = 3.
Abs(num): Returns absolute positive value. Example: abs(-10) = 10.
Formula for Random Range: Random(big - small + 1) + start.
Ceil/Floor Examples:
- Ceil(8.2) = 9
- Ceil(-3.1) = -3
- Floor(8.7) = 8
- Floor(-3.1) = -4

Programming Error Types

Syntax error: Errors in the use of the programming language (e.g., missing semicolon).
Logical error (Semantic error): Incorrect results produced due to a flawed algorithm.
Run-time error: Occurs while the program is running, potentially causing crashes (e.g., division by zero, square root of negative numbers).