# Logical expressions

Logical expressions (also called Boolean expressions) are
the result of applying logical (Boolean) operators to relational or
arithmetic expressions. The result of an operation has two possible
states: true or false. Logical expressions are considered false when
equal to 0, and are considered true when nonzero.

Logical operators have the lowest precedence and are evaluated
after all other operations have been evaluated. If two or more logical
operators appear in an expression, the leftmost operator is performed
first.

Logical operators act on their associated operands as
illustrated below:

| a or b is true (evaluates to 1) | if a is true or b is true. |
| --- | --- |
| a ! b is false (evaluates to 0) | if a and b are both false. |
| a and b is true (evaluates to 1) | only if both a and b are true. |
| a & b is false (evaluates to 0) | if a is false or b is false or both are false. |
The not() function negates the effect
of a logical expression:

| not(a or b) is true (evaluates to 1) | if a is false or b is false. |
| --- | --- |
| not(a and b) is true (evaluates to 1) | if a and b are false. |

## Example(s)

The then clause
is taken when `x` is a nonzero numeric. Whether `x` is a numeric constant, or an ASCII string, any nonzero
numeric value of `x` is true.

```
if x then...
```
This prints `An apple`, because `chr = "a"`.

```
word = "apple"
chr = word[1,1]
print "A":
print str("n",chr="a" or chr = "e" or chr = "i" or chr = "o" or chr = "u") :
print " ":word
```
In this example, the then clause is
executed if `visit.date` evaluates to a nonzero numeric.

```
visit.date = customer.item<5>
if visit.datethen...
```
The then clause is taken if `x` is between 1 and 10, exclusive.

```
if x > 1 and x < 10 then...
```
The then clause is taken if `x` is between either 1 and 10, exclusive, or between 100 and 200, inclusive.

```
if (x > 1 and x < 10) or (x >= 100 and x <= 200) then...
```
The printer on statement is executed
if the value of `print.flag` is not `n`.

```
if not(print.flag = "n") then printer on
```

## See also

- [! logical operator](https://d3codex.com/pickbasic-flashbasic/exclamation-logical-operator/)
- [and logical operator](https://d3codex.com/pickbasic-flashbasic/and-logical-operator/)
- [Arithmetic expressions](https://d3codex.com/pickbasic-flashbasic/arithmetic-expressions/)
- [Boolean evaluation](https://d3codex.com/pickbasic-flashbasic/boolean-evaluation/)
- [begin case statement](https://d3codex.com/pickbasic-flashbasic/begin-case-statement/)
- [Data representation](https://d3codex.com/pickbasic-flashbasic/data-representation/)
- [else clause](https://d3codex.com/pickbasic-flashbasic/else-clause/)
- [Expression](https://d3codex.com/definitions/expression/)
- [if statement](https://d3codex.com/pickbasic-flashbasic/if-statement/)
- [ifr statement](https://d3codex.com/pickbasic-flashbasic/ifr-statement/)
- [null statement](https://d3codex.com/pickbasic-flashbasic/null-statement/)
- [Precedence](https://d3codex.com/pickbasic-flashbasic/precedence/)
- [Relational operators](https://d3codex.com/pickbasic-flashbasic/relational-operators/)
- [String expressions](https://d3codex.com/pickbasic-flashbasic/string-expressions/)

---
Source: https://d3codex.com/pickbasic-flashbasic/logical-expressions/ - part of the D3Codex reference.