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Catalog / Delphi Programming Cheatsheet

Delphi Programming Cheatsheet

A concise reference for Delphi developers, covering essential syntax, data types, control structures, and object-oriented programming concepts.

Syntax and Basic Data Types

Program Structure 

program ProjectName;

uses
  // List of units (libraries) used by the program
  Forms, Dialogs;

{$APPTYPE GUI}

begin
  // Program execution starts here
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

Explanation:

  • program ProjectName; - Declares the program name.
  • uses - Specifies units (libraries).
  • {$APPTYPE GUI} - Compiler directive for GUI applications.
  • begin ... end. - The main program block.

Data Types

Integer

Signed integer. Common subtypes: Shortint, Smallint, Longint, Int64, Byte, Word, Longword.

Real

Floating-point number. Subtypes: Single, Double, Extended, Currency.

Char

Single character (e.g., 'A').

String

Sequence of characters. AnsiString (default), UnicodeString.

Boolean

True or False.

Variant

Can hold any data type; late binding.

Variable Declaration 

var
  VariableName: DataType;
  AnotherVariable: Integer;
  Name: String;

Explanation:

  • var - Keyword to declare variables.
  • VariableName - The name you choose for the variable.
  • DataType - The data type of the variable (e.g., Integer, String, Boolean).

Control Structures

Conditional Statements

If-Then-Else:

if condition then
begin
  // Code to execute if the condition is true
end
else
begin
  // Code to execute if the condition is false
end;

Case Statement:

case variable of
  value1: // Code to execute if variable = value1;
  value2: // Code to execute if variable = value2;
else
  // Code to execute if variable doesn't match any value
end;

Looping Constructs

For loop

 
for i := startValue to endValue do
begin
  // Code to execute in each iteration
end;

While loop

 
while condition do
begin
  // Code to execute while the condition is true
end;

Repeat-Until loop

 
repeat
  // Code to execute
until condition;

Break and Continue

  • Break: Exits the current loop.
  • Continue: Skips the rest of the current iteration and proceeds to the next.
 
for i := 1 to 10 do
begin
  if i = 5 then Continue; // Skips when i is 5
  if i = 8 then Break;    // Exits when i is 8
  ShowMessage(IntToStr(i));
end;

Procedures and Functions

Procedure Declaration 

procedure ProcedureName(Parameter1: DataType; Parameter2: DataType);
begin
  // Procedure body
end;

Explanation:

  • procedure - Keyword to declare a procedure.
  • ProcedureName - The name of the procedure.
  • (Parameter1: DataType) - Parameters passed to the procedure.

Function Declaration 

function FunctionName(Parameter1: DataType; Parameter2: DataType): ReturnType;
begin
  // Function body
  Result := ReturnValue; // Assign the return value
end;

Explanation:

  • function - Keyword to declare a function.
  • FunctionName - The name of the function.
  • (Parameter1: DataType) - Parameters passed to the function.
  • ReturnType - The data type of the value returned by the function.
  • Result - Special variable to assign the return value.

Parameters

Value parameters

Passed by value; changes to the parameter inside the procedure/function do not affect the original variable.

Var parameters

Passed by reference; changes to the parameter inside the procedure/function affect the original variable.

Const parameters

Passed by constant reference; optimized and prevents modification of the original variable.

Out parameters

Like var, but the initial value of the parameter is discarded. Used for returning values.

Object-Oriented Programming

Class Declaration 

type
  TMyClass = class(TObject)
  private
    // Private fields (data)
  protected
    // Protected fields and methods
  public
    // Public fields and methods
    constructor Create;
    destructor Destroy; override;
    procedure MyMethod;
  end;

Explanation:

  • type - Keyword to define a new type.
  • TMyClass - The name of the class (convention: start with T).
  • class(TObject) - Inherits from TObject (base class).
  • private, protected, public - Access specifiers.
  • constructor Create; - Constructor.
  • destructor Destroy; override; - Destructor (override required).

Methods

Constructor

 
constructor TMyClass.Create;
begin
  inherited Create;
  // Initialization code
end;

Destructor

 
destructor TMyClass.Destroy;
begin
  // Clean-up code
  inherited Destroy;
end;

Method

 
procedure TMyClass.MyMethod;
begin
  // Method implementation
end;

Inheritance 

type
  TMyDerivedClass = class(TMyClass)
  // ...
  end;

Explanation:

  • TMyDerivedClass inherits from TMyClass.
  • Derived classes inherit fields and methods from the base class.
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