Introduction to Lua - Learn Lua for iOS Game Development - page 11

Table 1-1. Arithmetic Operators

Operator Description

+ Addition

- Subtraction

*

Multiplication

/ Division

%

Modulo

^ Exponent

- Unary negation

Relational Operators
These are the operators used for comparing or conditions. They're listed in Table 1-2 .

Table 1-2. Relational Operators

Operator Description

== Equality (to check for equality between two values)

~=

Not equal to (the opposite of equality)

< Less than

> Greater than

<=

Less than or equal to

>= Greater than or equal to

These operators will always result in a true or a false return value. It should be noted that when
comparing two numbers or values, use the == where as a single = in Lua signifies assignment.

Logical Operators
The logical operators in Lua are

and
or
not

The way the and and or work in Lua is by what's called the shortcut evaluation . It checks for a value,
and checks further only if it is required. and returns the first arguments if the value is false or nil ; if it
isn't, then it returns the second argument. or , on the other hand, returns the first value if the result is
not false or nil , and returns the second argument if the first argument is false or nil .
The best use of or is in functions for assigning default values:
a = a or 5 -- Can be used to assign the value of 5 if the value of a is nil or false