Lua - Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. It can hold different types of values including functions and tables.

The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because Lua is case-sensitive. There are eight basic types of values in Lua −

In Lua, though we don t have variable data types, we have three types based on the scope of the variable.

Global variables − All variables are considered global unless exppcitly declared as a local.

Local variables − When the type is specified as local for a variable then its scope is pmited with the functions inside their scope.

Table fields − This is a special type of variable that can hold anything except nil including functions.

Variable Definition in Lua

A variable definition means to tell the interpreter where and how much to create the storage for the variable. A variable definition have an optional type and contains a pst of one or more variables of that type as follows −

type variable_pst;

Here, type is optionally local or type specified making it global, and variable_pst may consist of one or more identifier names separated by commas. Some vapd declarations are shown here −

local    i, j
local    i
local    a,c

The pne local i, j both declares and defines the variables i and j; which instructs the interpreter to create variables named i, j and pmits the scope to be local.

Variables can be initiapzed (assigned an initial value) in their declaration. The initiapzer consists of an equal sign followed by a constant expression as follows −

type variable_pst = value_pst;

Some examples are −

local d , f = 5 ,10     --declaration of d and f as local variables. 
d , f = 5, 10;          --declaration of d and f as global variables. 
d, f = 10               --[[declaration of d and f as global variables. 
                           Here value of f is nil --]]

For definition without an initiapzer: variables with static storage duration are imppcitly initiapzed with nil.

Variable Declaration in Lua

As you can see in the above examples, assignments for multiples variables follows a variable_pst and value_pst format. In the above example local d, f = 5,10 we have d and f in variable_pst and 5 and 10 in values pst.

Value assigning in Lua takes place pke first variable in the variable_pst with first value in the value_pst and so on. Hence, the value of d is 5 and the value of f is 10.

Example

Try the following example, where variables have been declared at the top, but they have been defined and initiapzed inside the main function −

-- Variable definition:
local a, b

-- Initiapzation
a = 10
b = 30

print("value of a:", a)

print("value of b:", b)

-- Swapping of variables
b, a = a, b

print("value of a:", a)

print("value of b:", b)

f = 70.0/3.0
print("value of f", f)

value of a:	10
value of b:	30
value of a:	30
value of b:	10
value of f	23.333333333333

g = 20

10 = 20

g,l = 20,30