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Variables (Delphi and Delphi Prism Cross Reference Guide)

By Mike Prestwood

Delphi versus Delphi Prism: A side by side comparison between Delphi and Delphi Prism.

 
Language Basics
 

Language basics is kind of a catch all for absolute beginner stuff. The items (common names) I chose for language basics is a bit random and include items like case sensitivity, commenting, declaring variables, etc.

Variables

[Other Languages] 

Languages Focus

A variable holds a value that you can use and change throughout your code so long as the variable is within scope. With variable declaration, you not only want to know the syntax of how you declare a variable but you also want to know where. Are you allowed to declare a variable inline? What are the available scopes: local vs. global. Can you assign a value at the same time you declare a variable?

Delphi:   var x: Integer = 0;

The Delphi language is a strongly typed language so you have to specifically declare variables and frequently use commands such as IntToStr and StrToInt.

Declare global variables in the interface section of a unit, variables declared within the implementation section (but not within a method) have a scope limited to the unit. You declare local variables in a var block outside (above) your begin..end code block. You cannot declare variables in-line (inside begin..end).

You can initialize global and unit variables but you cannot initialize local variables.

Delphi offers many variable types. Some common variable types include String, WideString, PCharInteger, Boolean, Single, Double, Pointer, and Variant.

Note: D2009 introduced a new UnicodeString type.

Syntax Example:
procedure SomeProcedure;
var
  Fullname: String;
  Age: Integer;
  X, Y, Z: Double;
  MyArray: array [1..100] of Char;
begin
end;
 
//You can initialize global variables.
var
  ClickCounter: Integer = 0;
Delphi Prism:   var x: Integer := 0;

Prism supports type inference where you just use a variable and the compiler will then choose the lowest type possible (such as an Integer before a LongInt). With Prism, you frequently do not have to use commands to convert from one type to another.

Variable names are not case sensitive. The Prism language offers both old-style declaring variables before the begin as well as in-line variable declaration.

Prism does support variable initialization too.

Prism offers many variable types. Some common variable types include Integer, LongInt, Single, Double, Boolean, and String.

Syntax Example:  
var
FName: String; //This is old-style.
begin
FName := "Mike Prestwood";
MessageBox.Show(FName);

Var Age: LongInt; //Local variables.
Age:=36;
MessageBox.Show(Fname + " is " + Age + " years old");

//Assign values too...
Var Wife: String:="Lisa"; Var WifeAge: Integer:=32;
messagebox.Show(wife + " is " + Wifeage + ".");
end;













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