Negation is the process of reversing the meaning of a Boolean expression. There are two approaches used to negate a Boolean expression.
First Approach
The first approach is the easiest one. Just use a NOT operator in front of the original Boolean expression and your negated Boolean expression is ready! For example,
PHP
if the original Boolean expression is $x > 5 && $y == 3,
the negated Boolean expression becomes !($x > 5 && $y == 3).
Notice: Please note that the entire expression must be enclosed in parentheses. It would be completely incorrect if you had written the expression without parentheses, as
!$x > 5 && $y == 3. In this case the NOT operator would negate only the first Boolean expression,$x > 5.
Java, C++, C#
if the original Boolean expression is x > 5 && y == 3,
the negated Boolean expression becomes !(x > 5 && y == 3).
Notice: Please note that the entire expression must be enclosed in parentheses. It would be completely incorrect if you had written the expression without parentheses, as
!x > 5 && y == 3. In this case the NOT operator would negate only the first Boolean expression,x > 5.
Visual Basic
if the original Boolean expression is x > 5 And y = 3,
the negated Boolean expression becomes Not (x > 5 And y = 3).
Notice: Please note that the entire expression must be enclosed in parentheses. It would be completely incorrect if you had written the expression without parentheses, as Not
x > 5 And y = 3. In this case the NOT operator would negate only the first Boolean expression,x > 5.
Python
if the original Boolean expression is x > 5 and y == 3,
the negated Boolean expression becomes not (x > 5 and y == 3).
Notice: Please note that the entire expression must be enclosed in parentheses. It would be completely incorrect if you had written the expression without parentheses, as not
x > 5 and y == 3. In this case the NOT operator would negate only the first Boolean expression,x > 5.
Second Approach
The second approach is a little bit more complex but not difficult to learn. All you must do is negate every operator according to the following table.
PHP
|
Original Operator |
Negated Operator |
|
== |
!= |
|
!= |
== |
|
> |
<= |
|
< |
>= |
|
<= |
> |
|
>= |
< |
|
&& |
|| |
|
|| |
&& |
|
! |
! |
Notice: Please note that the NOT operator ( ! ) remains intact.
For example,
if the original Boolean expression is $x > 5 && $y == 3,
the negated Boolean expression becomes $x <= 5 || $y != 3.
Java, C++, C#
|
Original Operator |
Negated Operator |
|
== |
!= |
|
!= |
== |
|
> |
<= |
|
< |
>= |
|
<= |
> |
|
>= |
< |
|
&& |
|| |
|
|| |
&& |
|
! |
! |
Notice: Please note that the NOT operator ( ! ) remains intact.
For example,
if the original Boolean expression is x > 5 && y == 3,
the negated Boolean expression becomes x <= 5 || y != 3.
Visual Basic
|
Original Operator |
Negated Operator |
|
= |
<> |
|
<> |
= |
|
> |
<= |
|
< |
>= |
|
<= |
> |
|
>= |
< |
|
And |
Or |
|
Or |
And |
|
Not |
Not |
Notice: Please note that the
Notoperator remains intact.
For example,
if the original Boolean expression is x > 5 And y = 3,
the negated Boolean expression becomes x <= 5 And y <> 3.
Python
|
Original Operator |
Negated Operator |
|
== |
!= |
|
!= |
== |
|
> |
<= |
|
< |
>= |
|
<= |
> |
|
>= |
< |
|
in |
not in |
|
not in |
in |
|
and |
or |
|
or |
and |
|
not |
not |
Notice: Please note that the
notoperator remains intact.
For example,
if the original Boolean expression is x > 5 and y == 3,
the negated Boolean expression becomes x <= 5 or y != 3.