Basic Syntax & Data Types

1. Program Structure and Flow

Object Pascal is a highly structured language. Code execution typically flows from the entry point (.dpr file) into the main units (.pas). Within units, code execution is governed by begin and end blocks.

• Execution Block: All executable code must be contained within a begin and end; pair.
• Case Insensitivity: Object Pascal is largely case-insensitive for keywords and identifiers (e.g., Begin, BEGIN, and begin are all treated the same, but it is best practice to use standard casing).
• Statement Termination: Unlike C-style languages that use the semicolon (;) to end a statement, Pascal uses the semicolon as a statement separator. It is placed between statements, but not before an end or else keyword.

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage('Statement 1'); // Statement 1 followed by semicolon
  ShowMessage('Statement 2') // Statement 2, no semicolon before end
end;

2. Variables

Variables are memory locations used to store data. In Object Pascal, variables must be declared before they can be used, and they are defined within a dedicated var block.

Declaration Syntax

The syntax for declaration is: VariableName: DataType;

procedure TForm1.FormCreate(Sender: TObject);
var
  // Variables declared within a procedure are local to that procedure
  UserName: String;
  UserAge: Integer;
begin
  UserName := 'Alice'; // Assignment operator is :=
  UserAge := 30;
  
  ShowMessage('Hello, ' + UserName);
end;

3. Basic Data Types

Object Pascal is a strongly-typed language, meaning a variable can only hold values that match its declared type.

A. Integer Types (Whole Numbers)

Used for counting, indices, and sizes. They are optimized for speed.

B. Real Types (Floating Point)

Used for numbers with fractional parts.

C. String Types (Text)

Delphi uses modern Unicode strings by default.

D. Boolean Type

Used for logical testing and decision making.

4. Constants

Constants are identifiers whose values are fixed at compile time and cannot be changed during program execution.

• Syntax: Defined within a dedicated const block.
• Benefit: Improves readability and ensures consistency (e.g., a fixed tax rate used throughout an application).

procedure TForm1.FormCreate(Sender: TObject);
const
  // Constants must be initialized immediately
  TaxRate = 0.05; 
  AppTitle = 'Inventory Manager';
  MaxUsers: Integer = 100; // Type is optional for simple types
begin
  ShowMessage('Welcome to ' + AppTitle);
end;

5. Type Casting and Conversion

Since Object Pascal is strongly typed, you must explicitly convert data between different types.

• Type Casting (Hard Cast): Used when you are certain the conversion is safe (common with object pointers or low-level memory). Syntax: NewType(Expression)
• Conversion Functions (Soft Cast): Used for converting between strings and numbers (safer).

var
  S: String;
  I: Integer;
  R: Double;
begin
  I := 123;
  R := 45.67;

  // Numerical to String Conversion
  S := IntToStr(I);    // S is '123'
  S := FloatToStr(R);  // S is '45.67'

  // String to Numerical Conversion
  I := StrToInt('10'); // I is 10
  R := StrToFloat('9.99'); // R is 9.99
  
  // Hard Cast (Example: converting an integer to a byte type)
  var B: Byte;
  B := Byte(I); // Assuming I is a value between 0 and 255
end;