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Lua basic tutorial

Lua Operators

An operator is a special symbol used to tell the interpreter to perform a specific mathematical or logical operation. Lua provides the following types of operators:

  • Arithmetic operators

  • Relational operators

  • Logical operators

  • Other operators

Arithmetic operators

The following table lists the commonly used arithmetic operators in the Lua language, setting the value of A to10, the value of B is 20:

OperatorDescriptionExample
+AdditionA + B output result 30
-SubtractionA - B output result -10
*MultiplicationA * B output result 200
/DivisionB / A w output result 2
%ModuloB % A output result 0
^PowerA^2 Output result 100
-Negative sign-A output result -10

Online Example

We can understand the application of arithmetic operators more thoroughly through the following examples:

a =　21
b =　10
c = a　+　b
print("Line　1　-　The value of c is " , c )
c = a　-　b
print("Line　2　-　The value of c is " , c )
c = a　*　b
print("Line　3　-　The value of c is " , c )
c = a　/　b
print("Line　4　-　The value of c is " , c )
c = a % b
print("Line　5　-　The value of c is " , c )
c = a^2
print("Line　6　-　The value of c is " , c )
c =　-a
print("Line　7　-　The value of c is " , c )

The result of the above program is:

Line　1　-　The value of c is　　　　　31
Line　2　-　The value of c is　　　　　11
Line　3　-　The value of c is　　　　　210
Line　4　-　The value of c is　　　　　2.1
Line　5　-　The value of c is　　　　　1
Line　6　-　The value of c is　　　　　441
Line　7　-　The value of c is　　　　　-21

Relational operators

The following table lists the commonly used relational operators in the Lua language, setting the value of A to10, the value of B is 20:

OperatorDescriptionExample
==Equal, checks if two values are equal, returns true if they are equal, otherwise returns false(A == B) is false.
~=Not equal, checks if two values are equal, returns true if they are not equal, otherwise returns false(A ~= B) is true.
>Greater than, returns true if the value on the left is greater than the value on the right, otherwise returns false(A > B) is false.
<Less than, returns false if the value on the left is greater than the value on the right, otherwise returns true(A < B) is true.
>=Greater than or equal to, returns true if the value on the left is greater than or equal to the value on the right, otherwise returns false(A >= B) returns false.
<=Less than or equal to, returns true if the value on the left is less than or equal to the value on the right, otherwise returns false(A <= B) returns true.

Online Example

We can understand the application of relational operators more thoroughly through the following examples:

a =　21
b =　10
if( a == b )
then
　　　print("Line　1　-　a equals b" )
else
　　　print("Line　1　-　a does not equal b" )
end
if( a ~= b )
then
　　　print("Line　2　-　a does not equal b" )
else
　　　print("Line　2　-　a equals b" )
end
if(a < b)
then
　　　print("Line　3　-　a is less than b)
else
　　　print("Line　3　-　a is greater than or equal to b)
end
if(a > b)　
then
　　　print("Line　4　-　a is greater than b)
else
　　　print("Line　5　-　a is less than or equal to b)
end
--　Modify the values of a and b
a =　5
b =　20
if(a <= b)　
then
　　　print("Line　5　-　a is less than or equal to b)
end
if(b >= a)　
then
　　　print("Line　6　-　b is greater than or equal to a)
end

The result of the above program is:

Line　1　-　a is not equal to b
Line　2　-　a is not equal to b
Line　3　-　a is greater than or equal to b
Line　4　-　a is greater than b
Line　5　-　a is less than or equal to b
Line　6　-　b is greater than or equal to a

Logical operators

The following table lists the commonly used logical operators in the Lua language, with A set to true and B set to false:

OperatorDescriptionExample
andLogical AND operator. If A is false, it returns A, otherwise it returns B.(A and B) is false.
orLogical OR operator. If A is true, it returns A, otherwise it returns B.(A or B) is true.
notLogical NOT operator. It is the opposite of the logical operation result, if the condition is true, logical NOT is false.not(A and B) is true.

Online Example

We can understand the application of logical operators more thoroughly through the following examples:

a = true
b = true
if(a and b)
then
　　　print("a and b　-　Condition is true)
end
if(a or b)
then
　　　print("a or b　-　Condition is true)
end
print("---------Separator---------"
--　Modify the values of a and b
a = false
b = true
if(a and b)
then
　　　print("a and b　-　Condition is true)
else
　　　print("a and b　-　Condition is false)
end
if(not(a and b))
then
　　　print("not(a and b)　-　Condition is true)
else
　　　print("not(a and b)　-　Condition is false)
end

The result of the above program is:

a and b　-　Condition is true
a or b　-　Condition is true
---------Separator---------
a and b　-　Condition is false
not(a and b)　-　Condition is true

Other operators

The following table lists the concatenation operators and operators for calculating table or string length in the Lua language:

OperatorDescriptionExample
..Concatenate two stringsa..b, where a is "Hello " and b is "World", the output is "Hello World".
#Unary operator, returns the length of the string or table.#"Hello" returns 5

Online Example

We can understand the application of the concatenation operator and the operator for calculating table or string length more thoroughly through the following examples:

a = "Hello "
b = "World"
print("Concatenate strings a and b", a..b )
print("b string length", #b )
print("The length of the string 'Test' ", #"Test")
print("The length of the Basic Tutorial website URL ", #"www.w")3codebox.com"

The result of the above program is:

Concatenate strings a and b 'Hello World'
The length of string b　　　　　5
The length of the string 'Test'　　　　　4
The length of the Basic Tutorial website URL　　　　　14

Operator Precedence

In order from high to low:

^
not　　　　-　(unary)
*　　　　　　/　　　　　　　%
+　　　　　　-
..
< > <= >= ~= ==
and
or

All binary operators except ^ and .. are left-associative.

a+i < b/2+1　　　　　　　　　　<--> x^(a < y) and (y <= z)+i) < ((b/2)+1)
5+x^2*8　　　　　　　　　　　　　　<-->　　　　　　　5+((x^2)*8)
x^(y^z) <--> x^(y^z) <
-x^2　　　　　　　　　　　　　　　　　<-->　　　　　　　-(x^2)
x^y^z <--> x^(y^z)

Online Example

We can use the following examples to better understand the precedence of Lua language operators:

a =　20
b =　10
c =　15
d =　5
e = (a　+　b)　*　c　/　d;--　(　30　*　15　)　/　5
print("(a　+　b)　*　c　/　d) The value of:
e = ((a　+　b)　*　c)　/　d;　--　(30　*　15　)　/　5
print("((a　+　b)　*　c)　/　d) The value of:
e = (a　+　b)　*　(c　/　d);--　(30)　*　(15/5)
print("(a　+　b)　*　(c　/　d) The value of:
e = a　+　(b　*　c)　/　d;　　--　20　+　(150/5)
print("a　+　(b　*　c)　/　d) The value of:

The result of the above program is:

(a　+　b)　*　c　/　d) The value of:　　　　90.0
((a　+　b)　*　c)　/　d) The value of:　　　　90.0
(a　+　b)　*　(c　/　d) The value of:　　　　90.0
a　+　(b　*　c)　/　The value of d is:　　　　50.0
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