From 5.3 (non character examples skipped)
//
<> != #
Not equal--binary (Relational)
Syntax
<exp1> <> <exp2>
<exp1> != <exp2>
<exp1> # <exp2>
Type
Character, date, logical, memo, NIL, numeric
Operands
<exp1> and <exp2> are expressions of the same data type or NIL
to be compared for inequality.
Description
The not equal ( <>) operator compares two values of the same data type
and returns true (.T.) if <exp1> is not equal to <exp2> according to the
following rules:
. Character: The comparison is based on the underlying ASCII
code and is the inverse of the equal operator (=). This means that
the comparison is sensitive to the current EXACT SETting. See the
examples below.
Examples
. These examples illustrate how the not equal operator (<>)
behaves with different data types:
// Character
SET EXACT ON
? "123" <> "12345" // Result: .T.
? "12345" <> "123" // Result: .T.
? "123" <> "" // Result: .T.
? "" <> "123" // Result: .T.
SET EXACT OFF
? "123" <> "12345" // Result: .T.
? "12345" <> "123" // Result: .F.
? "123" <> "" // Result: .F.
? "" <> "123" // Result: .T.
//
= (equality)
Equal--binary (Relational)
Syntax
<exp1> = <exp2>
Type
Character, date, logical, memo, NIL, numeric
Operands
<exp1> and <exp2> are expressions of the same data type to
compare.
Description
The equal operator (= ) compares two values of the same data type and
returns true (.T.) if <exp1> is equal to <exp2> according to the
following rules:
. Character: The comparison is based on the underlying ASCII
code. ASCII codes for alphabetic characters are ascending (e.g., the
code for "A" is 65 and the code for "Z" is 90).
When EXACT is OFF, two character strings are compared according to
the following rules. assume two character strings, cLeft and cRight,
where the expression to test is (cLeft = cRight):
- If cRight is null, returns true (.T.).
- If LEN(cRight) is greater than LEN(cLeft), returns false
(.F.).
- Compare all characters in cRight with cLeft. If all
characters in cRight equal cLeft, returns true (.T.); otherwise,
returns false (.F.).
With EXACT ON, two strings must match exactly except for trailing
blanks.
Examples
. These examples illustrate how the equal operator (=) behaves
with different data types:
// Character
SET EXACT ON
? "123" = "123 " // Result: .T.
? " 123" = "123" // Result: .F.
SET EXACT OFF
? "123" = "12345" // Result: .F.
? "12345" = "123" // Result: .T.
? "123" = "" // Result: .T.
? "" = "123" // Result: .F.
//
==
Exactly equal--binary (Relational)
Syntax
<exp1> == <exp2>
Type
All
Operands
<exp1> and <exp2> are expressions of the same data type to be
compared.
Description
The exactly equal operator (==) is a binary operator that compares two
values of the same data type for exact equality depending on the data
type. It returns true (.T.) if <exp1> is equal to <exp2> according to
the following rules:
. Array: Compares for identity. If <exp1> and <exp2> are
variable references to the same array, returns true (.T.); otherwise,
returns
false (.F.).
. Character: Comparison is based on the underlying ASCII code.
ASCII codes for alphabetic characters are ascending (e.g., the code
for "A" is 65 and the code for "Z" is 90). Unlike the relational
equality operator (=) , true (.T.) is returned if <exp1> and <exp2>
are exactly equal including trailing spaces; otherwise, the
comparison returns false (.F.). SET EXACT has no effect.
Examples
. These examples illustrate how the == operator behaves with
different data types:
// Character
? "A" == "A" // Result: .T.
? "Z" == "A" // Result: .F.
? "A" == "A " // Result: .F.
? "AA" == "A" // Result: .F. 
