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Comparison Operators (Cross Ref > Operators)

Comparison Operators

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.

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

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

ASP Classic: =, <>

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 ASP evaluate the math correctly? No!

If .1 + .1 + .1 = .3 Then
  Response.Write "correct"
Else
  Response.Write "not correct"
End If

ASP Classic Comparison Operators (=, <>)

The Fix

There are several techniques for handling computer rounding errors. For ASP Classic, consider using the Round function. For example:

If Round(.1+.1+.1, 4) = .3 Then
  Response.Write "yes" & "&lt;br&gt;"  'Yes is displayed!
Else
  Response.Write "no" & "&lt;br&gt;"
End If

Reserve Floating Point Values

Because computers have trouble representing floating point values, you may want to reserve the use of floating point literals for imprecise measurements such length, height, weight, etc. The very nature of measurements is imprecise.

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

C#: ==, !=

Common comparison operators:

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

Syntax Example:

//Does C# evaluate the math correctly? No!

if (.1 + .1 + .1 == .3)
  MessageBox.Show("correct");
else
  MessageBox.Show("not correct");

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

C++: ==, !=

Common comparison operators:

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

Syntax Example:

//C++Builder example (ShowMessage is a VCL method).

//Does C++Builder evaluate the math correctly? No!

If (.1 + .1 + .1 == .3)
  ShowMessage("correct");
else
  ShowMessage("not correct");

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

C++/CLI: ==, !=

Same as standard C++. Common comparison operators:

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

Syntax Example:

//Does C++/CLI evaluate the math correctly? No!

if (0.1 + 0.1 + 0.1 == 0.3)
  MessageBox::Show("correct");
else
  MessageBox::Show("not correct");

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

Corel Paradox: =, <>

Common comparison operators:

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

Syntax Example:

'Does ObjectPAL evaluate the math correctly? No!

If .1 + .1 + .1 = .3 Then
  msgInfo("", "correct")
Else
  msgInfo("", "not correct")
endIf

ObjectPAL Comparison Operators (=, <>)

Overcoming Floating Point Errors

Because computers have trouble with certain floating point values (such as .1), you need to decide what level of accuracy is "good enough" for your application. Perhaps establish a standard for each application. For example, you could establish 6 decimal points as a standard and require all developers to use ObjectPAL's round() method when comparing floating point number. For example, you could rewrite the above routine as follows and get the result you expect.

If round(.1 + .1 + .1, 6) = round(.3, 6) Then
  msgInfo("", "correct")
Else
  msgInfo("", "not correct")
EndIf

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Code:	ObjectPAL Comparison Operators (=, <>)
Tip:	Round Floating Point Numbers

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')

Delphi Comparison Operators (=, <>)

Delphi 2009 Working Example

Here's a simple working example from a button click event:

procedure TForm1.Button1Click(Sender: TObject);
var
  x: Boolean;
begin
  x := True;

  if x = True then
  begin
    ShowMessage('X was true');
  end
  else
  begin
    ShowMessage('X was false');
  end;
end;

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Code:	Delphi Comparison Operators (=, <>)
Tip:	Round Floating Point Numbers

Delphi Prism: =, <>

Same as Delphi. Common comparison operators:

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

Syntax Example:

//Does Prism evaluate the math correctly? No!

//This is different than later versions of

//Delphi that muse MaxSingle in math.pas.

If .1 + .1 + .1 = .3 Then
  MessageBox.Show("correct")
Else
  MessageBox.Show("not correct");

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

Java: ==, !=

The Java comparison operators are:

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

More Info / Comment

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

JavaScript: ==, !=

Common comparison operators:

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

Syntax Example:

//Does JavaScript evaluate the math correctly? No!

if (.1 + .1 + .1 == .3) {
  document.write("correct");
}
else {
  document.write("not correct");
}

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

Perl: ==, !=

Common comparison operators:

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

Perl also offers additional string comparison operators:

eq	string equals
ne	string not equal
lt	string less than
gt	string greater than
le	string less than or equal
ge	string greater than or equal

Syntax Example:

#Does Perl evaluate the math correctly? No!

if ((.1 + .1 + .1) == .3) {
  print("Correct<br>");
} else {
  print("Not correct<br>");
}

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

PHP: ==, != or <>

Common comparison operators:

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

PHP 4 and above also offers === for indentical (equal plus same type) and !== for not identical (not equal or not same type).

Syntax Example:

//Does PHP evaluate the math correctly? No!

if (.1 + .1 + .1 == .3) {
  echo "correct";
}
else {
  echo "not correct";
}

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

VB Classic: =, <>

Common comparison operators:

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

Syntax Example:

//Does VB evaluate the math correctly? No!

If 0.1 + 0.1 + 0.1 = 0.3 Then
  MsgBox "correct"
Else
  MsgBox "not correct"
End If

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers

VB.Net: =, <>

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 VB.Net evaluate the math correctly? No!

If 0.1 + 0.1 + 0.1 = 0.3 Then
  MessageBox.Show("correct")
Else
  MessageBox.Show("not correct")
End If

Linked Certification Question(s)

The following are practice certification questions with answers highlighted. These questions were prepared by Mike Prestwood and are intended to stress an important aspect of this KB post. All our practice questions are intended to prepare you generally for passing any certification test as well as prepare you for professional work.

Beginner

1 Beginner Level Question

Question #1: Multiple Choice

Which code statement is the correct use of the comparison operator?

Answer:

If x == True Then

  MessageBox.Show("x is true")

End If

If (x = True)

  MessageBox.Show("x is true")

End If

If (x == True)

  MessageBox.Show("x is true")

End If

If (x == True) Then

  MessageBox.Show("x is true")

End If

If x = True Then

  MessageBox.Show("x is true")

End If

More Info

To/From Code Guide: Comparison Operators (Cross Ref > Operators) vs. Other Languages

Tip:	Round Floating Point Numbers