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Cross Ref > Operators

By Mike Prestwood

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

 
Operators
 

A language symbol used for assignment, comparison, computational, or as a logical.

Assignment

[Other Languages] 

Languages Focus

Common assignment operators for languages include =, ==, and :=. An assignment operator allows you to assign a value to a variable. The value can be a literal value like "Mike" or 42 or the value stored in another variable or returned by a function.

Delphi:   :=

Delphi uses := for it's assignment operator.

Syntax Example:
var
  FullName: String;
  Age: Integer;
begin
  FullName := "Randy Spitz";
Age := 38;
end
Access VBA:   =

Access uses = for it's assignment operator.

Syntax Example:
Dim Age As Integer
Dim FullName As String
   
FullName = "Randy Spitz"
Age = 38




Comparison Operators

[Other Languages] 

General Info: Round Floating Point Numbers

When comparing floating point numbers, make sure you round to an acceptable level of rounding for the type of application you are using.

Languages Focus

A comparison operator compares two values either literals as in "Hello" and 3 or variables as in X and Counter. Most languages use the same operators for comparing both numbers and strings. Perl, for example, uses separate sets of comparison operators for numbers and strings.

Delphi:   =, <>

Common comparison operators:

= equal
<> not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

Syntax Example:
//Does Delphi evaluate the math correctly? Yes!
//Refer to math.pas MaxSingle for more info.
if (0.1 + 0.1 + 0.1 = 0.3) then
ShowMessage('correct')
else
ShowMessage('not correct')
Access VBA:   =, <>

Save as VB Classic. Common comparison operators:

= equal
<> not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

Syntax Example:
//Does Access evaluate the math correctly? No!
If 0.1 + 0.1 + 0.1 = 0.3 Then
MsgBox "correct"
Else
MsgBox "not correct"
End If




Empty String Check

[Other Languages] 

Languages Focus

An empty string is a zero length string, a string that is equal to null (""), or not assigned. In some languages, you can check if a string is empty by comparing it to an empty string (""). Some languages distinguish between nil and null ("") so checking if the length is 0 is easier.

Delphi:   length(s) = 0

Length() or SizeOf() will correctly identify an unassigned string variable or an empty string.

Syntax Example:
if length(s) = 0 then
  ShowMessage('empty string');
Access VBA:   Len(s&vbNullString)

In Access VBA, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

Syntax Example:

All these will work for variables unassigned, set to "", or set to Null:

If s&"" = "" Then
  MsgBox ("Quotes with &'' say null is empty")
End If
 
If Len(s&"") = 0 Then
  MsgBox ("Len with &'' says null is empty")
End If
 
If Len(s&vbNullString) = 0 Then
  MsgBox ("Using vbNullString also works!")
End If




Logical Operators

[Other Languages] 

Languages Focus

Logical operators perform conditional and, or, and not operations. Some languages support both binary logical operators that link two and unary logical operators negate (make opposite) the truth value of its argument. Finally, some languages short circuit logic. For example, with this or that, if this is an expression returning true, then that is never executed.

Delphi: 

Delphi logical operators:

and and, as in this and that
or or, as in this or that
not Not, as in Not This
xor either or, as in this or that but not both

The Delphi compiler default is to short circuit multi argument boolean expressions when the result is known before the evaluation completes. To disable short circuiting, use the {$B+} compiler directive. To reset it back to the compiler default of short circuting, use the {$B-} compiler directive.

Syntax Example:
//Given expressions a, b, c, and d:
if Not (a and b) and (c or d) then
  //Do something.
Access VBA:   and, or, not

Same as VB. Access VBA logical operators:

and and, as in this and that
or or, as in this or that
Not Not, as in Not This

Access VBA never short circuits. Given the expression this or that as well as this and that, if this evaluates to false, then that is still executed.

Syntax Example:
'Given expressions a, b, c, and d:
If Not (a and b) and (c or d) Then
  'Do something.
End If




String Concatenation

[Other Languages] 
Delphi:  "String Concatenation" +

Use the + operator to concatenate two strings. Use IntToStr to convert an integer to a string and FloatToStr to convert a floating point number to a string.

Syntax Example:
var 
  FirstName : String; 
  LastName : String;
begin 
  FirstName := 'Mike'; 
  LastName := 'Prestwood';
  ShowMessage('Full name: ' + FirstName + ' ' + LastName);
  
  ShowMessage(FloatToStr(3.2));
end;
Access VBA:  "String Concatenation" & or +

Although you can use either a & or a + to concatenate values, my preference is to use a + because more languages use it. However, if you use & then some type conversions are done for you. If you use + you will sometimes have to cast a value to concatenate it. For example, you will have to use CStr to cast a number to a string if you use the + operator as a concatenation operator.

Syntax Example:
Dim FirstName As String
Dim LastName As String
 
FirstName = "Mike"
LastName = "Prestwood"
 
MsgBox "Full name: " & FirstName & " " & LastName
 
MsgBox "2+2=" + CStr(2+2)




Unary Operators

[Other Languages] 

General Info: Unary Operator

An operation with only one operand (a single input). Common unary operators include + plus, - minus, and bitwise not. Some operators can function as both unary and binary operators. For example, + and - operators can serve as either.

Languages Focus

What unary operators are supported in additoin to the standard plus, minus, and bitwise not.

Delphi: 

An operation with only one operand (a single input). In Object Pascal, a unary operator has the highest precedence and always precedes its operand (for example, -B), except for the  ^ pointer operator, which follows its operand (for example, P^). In addition to the obvious +, -, and Not operators, Delphi also offers:

^ Pointer
@ returns the address of a variable, function, procedure, or method; a pointer to its operand.
inc() Increment
dec() Decrement

The TYPE operator is also a unary operator and is valuated at compile time. The TYPE operator returns the size in bytes of the operand,

More Info / Comment
Access VBA: 

An operation with only one operand (a single input) such as +, -, and Not.






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