# Boolean expression facts for kids

In computer science, a **Boolean expression** is an expression used in programming languages that produces either **true** or **false** when evaluated. Boolean expressions are often used by conditionals in computer programs to decide which code to run.

Most Boolean expressions will contain at least one variable (

), and often more (`X > 3`

) so that the expression can be useful for various values of X and Y.`X > Y`

## Boolean operators

Boolean operators may be represented by words such as OR, AND and *NOT*.

Some programming languages use symbols such as "||" (double pipe character) for OR, "&&" (double ampersand) for AND, and "!" for NOT. Other programming languages may use other symbols.

Other Boolean operators may be available, too, for example XOR (exclusive OR).

Boolean expressions can also be represented as Logic gates in electronic circuit diagrams.

See Truth tables for a summary of the effects of common Boolean operators.

## Examples

- The expression

evaluates as`5 > 3`

`true`. - The expression

evaluates as`3 > 5`

`false`. - The expression

evaluates as`(X > 3) AND (X < 5)`

`true`for any value of X between 3 and 5. - The expression

evaluates as`(X <= 3) OR (X >= 5)`

`true`for any value of X which less than or equal to 3 or is greater than or equal to 5, in other words any value of X which is*not*between 3 and 5. - The English language expression "any value of X which is
*not*between 3 and 5" can be represented as

.`NOT ((X > 3) AND (X < 5))`

## An exercise for the reader

- Try evaluating

using X=4 and again using X=6.`NOT ((X > 3) AND (X < 5))`

- For X=6, it is
`true`that X is not between 3 and 5. - For X=4, it is
`false`that X is*not*between 3 and 5 because 4*is*between 3 and 5.

- For X=6, it is

*Kiddle Encyclopedia.*