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   ► KBTo/From GuidesDelphi PrismLanguage Basics  Print This     

Cross Ref > Language Basics

By Mike Prestwood

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

 
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.

Case Sensitivity

[Other Languages] 

Languages Focus

Case sensitiviy in this case is referring to commands and variable names. For example, are "printf" and "PrintF" equivalent? Are fullname and FullName equivalent? When you create commands, operations, methods, or variables should you worry about case?

Delphi Prism:   No

Prism is generally not case sensitive. Commands and variable names are not case sensitive.

Note: Prism (and Delphi for .Net) do not automatically match your typed case with the defined case as C# and VB.Net do within the Visual Studio Shell.

Syntax Example:  

The following demonstrates command and variable case insensitiviy.

var
 FullName: String;
begin
 fullname := 'Mike Prestwood';
 MessageBox.Show(fullNAME);
 MESSAGEBOX.SHOW(FULLNAME);
 messAGEbox.sHow(fullname);
end;
Access VBA:   No

Access VBA is not case sensitive. Like VB Classic, if you type any other case for command or variable names, Access VBA will change it to the "accepted" or "defined" case. For example, if you type msgbox it is converted to Msgbox.

Syntax Example:  

The following code works:

MsgBox ("hello")




Code Blocks

[Other Languages] 

Languages Focus

The rules for code blocks within a language dictate where you can declare variables, how you "bracket" code, etc.

Delphi Prism:   begin..end

Same as in Delphi for Win32 but Prism also supports inline variable declaration.

Syntax Example:
function DoSomething : integer;
var
 a, b : integer;
begin
 a := 1;
 b := 2;
 var c : integer; //Prism allows inline (local) variables.
 c := a + b;
  
 result := c;
end;
Access VBA:   End Xxx

Access VBA code blocks are surrounded by statement ending keywords that all use End such as End Sub, End If, and WEnd.

Syntax Example:
Sub x
End Sub
 
If x Then
End If
  
While x
WEnd




Comments

[Other Languages] 

Languages Focus

Commenting code generally has three purposes: to document your code, for psuedo coding prior to coding, and to embed compiler directives. Most languages support both a single line comment and a multiple line comment. Some languages also use comments to give instructions to the compiler or interpreter.

Delphi Prism:   // or { ... } or (* ... *)

Commenting Code
Delphi uses // for a single line comment and both {} and (**) for multiple line comments. Although you can nest different types of multiple line comments, it is recommended that you don't.

Compiler Directives - $
A special comment. Delphi compiler directives are in the form of {$DIRECTIVE}. Of interest for comments is using the $IFDEF compiler directive to remark out code.

Syntax Example:
//This is a single line comment.
 
{
Multiple line
comment.
}
 
(*
This too is a
multiple line comment.
*)
 
{$IFDEF TEMPOUT}
//...code here
{$ENDIF}
Access VBA:   ' or REM

Commenting Code
Access VBA, like all the VB-based languages, uses a single quote (') or the original class-style basic "REM" (most developers just use a quote). Access VBA does NOT have a multiple line comment.

Directives - #

Directives are sometimes called compiler or preprocessor directives. A # is used for directives within Access VBA code. Access VBA offers only an #If..then/#ElseIf/#Else directive.

Syntax Example:
'Single line comment.

REM Old school single line comment.

#If MyDirective Then
'...some code.
#End If




Constants

[Other Languages] 

General Info: Computer Language Constants

A constant is just like a variable (it holds a value) but, unlike a variable, you cannot change the value of a constant.

Delphi Prism:   const kPI: Double=3.1459;

In Prism, you define constants similar to how you define variables but use the Const keyword instead of the Var keyword. Specifying the type is optional. If you don't specify the type, the compiler chooses the most appropriate type for you.

Declare class constants as part of the class definitions. Declare local constants above the begin..end. Although Prism support inline variables, inline constants are not supported.

Syntax Example:
//Specified type:
const
kFeetToMeter: Double = 3.2808;
  kMeterToFeet: Double = .3048; 
  kName: String = "Mike";

//Unspecified type:
const kPIShort = 3.14;
Access VBA:   Const kPI = 3.1459

Scope can be Public, Global, or Private. The use of the newer Public keyword is preferred to the older Global. Private Const is the same as just specifying Const.

Syntax Example:
Const kPI = 3.1459
Const kName = "Mike"
 
//Public variable:
Public Const kFeetToMeter=3.28, kMeterToFeet=.3




End of Statement

[Other Languages] 

Languages Focus

In coding languages, common End of statement specifiers include a semicolon and return (others exist too). Also of concern when studying a language is can you put two statements on a single code line and can you break a single statement into two or more code lines.

Delphi Prism:   ;

Object Pascal uses a semicolon ";" as an end of statement specifier and you can put multiple statements on a single line of code and put a single statement on two or more code lines if you wish.

Syntax Example:  
MessageBox.Show("Hello1");
MessageBox.Show("Hello2");
MessageBox.Show("Hello3");

//Same line works too:
MessageBox.Show("Hello4");  MessageBox.Show("Hello5");

//Two or more lines works too:
MessageBox.Show
("Hello6");
Access VBA:   Return

A return marks the end of a statement and you cannot combine statements on a single line of code. You can break a single statement into two or more code lines by using a space and underscore " _".

Syntax Example:
MsgBox "Hello1"
MsgBox "Hello2"
MsgBox "Hello3"

'The following commented code on a single line does not work...
'MsgBox "Hello4" MsgBox "Hello5"

'Two or more lines works too with a space+underscore:
MsgBox _
"Hello6";




Literals

[Other Languages] 

General Info: Programming Literals

A value directly written into the source code of a computer program (as opposed to an identifier like a variable or constant). Literals cannot be changed. Common types of literals include string literals, floating point literals, integer literals, and hexidemal literals. Literal strings are usually either quoted (") or use an apostrophe (') which is often referred to as a single quote. Sometimes quotes are inaccurately referred to as double quotes.

Languages Focus

In addition to understanding whether to use a quote or apostrophe for string literals, you also want to know how to specify and work with other types of literals including floating point literals. Some compilers allow leading and trailing decimals (.1 + .1), while some require a leading or trailing 0 as in (0.1 + 0.1). Also, because floating point literals are difficult for compilers to represent accurately, you need to understand how the compiler handles them and how to use rounding and trimming commands correctly for the nature of the project your are coding.

Delphi Prism:   quote or apostrophe

In Prism, you use either quotes or apostrophes for string literals.

Different than Delphi, you can start floating point literals with a decimal or an integer. For example, to specify a fractional floating point literal between 1 and -1, you can preceed the decimal with a 0 or not.

x := .1 + .1;     //Does work.
x := 0.1 + 0.1;   //Does work.
Syntax Example:  
MessageBox.Show('Hello');
MessageBox.Show("Hello");

//Example of embedding quotes and apostropes:
MessageBox.Show('He said, "Who''s computer?"');
MessageBox.Show("She said, ""Mike's computer"".");
Access VBA:   quote

String literals are quoted as in "Prestwood". If you need to embed a quote use two quotes in a row.

To specify a floating point literal between 1 and -1, you can preceed the decimal with a 0 or not (both work). In other words, preceding and following decimals are allowed (both .1 and 0.1). Trailing decimals are optimized out and replaced with # if only integer values are used.

Syntax Example:
MsgBox ("Hello")
MsgBox ("Hello ""Mike"".")
 
'Does Access VBA evaluate this simple
'floating point math correctly? No! 
If (.1 + .1 + .1) = 0.3 Then
MsgBox "Correct"
Else
MsgBox "Not correct"
End If




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 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;
Access VBA:   Dim x as Integer

Access VBA is a loosely typed language. Declaring variables is optional unless you use the Option Explicit statement to force explicit declaration of all variables with Dim, Private, Public, or ReDim. Using Option Explicit is strongly recommended to avoid incorrectly typing an existing variable and to avoid any confusion about variable scope.

Undeclared variables are variants. To specifically declare a variant, use:

Dim x As Variant
Dim x 

Common data types include Byte (0..255), Boolean, Integer (2-byte integers), Long (4-byte integers), Currency, Single (32-bit number), Double (64-bit number), Date, String, and variant.

Variables declared with Dim at the module level are available to all procedures within the module. At the procedure level, variables are available only within the procedure.

Syntax Example:
Dim FullName As String
Dim Age As Integer
Dim Weight As Double
 
FullName = "Mike Prestwood"
Age = 32
Weight = 154.4
 
'Declaritive assignment not supported:
''Dim Married As String = "Y"   '>>>Not supported.




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