4.18. Lua operator

An operator is a special symbol that tells the interpreter to perform specific mathematical or logical operations. Lua provides the following types of operators:

Arithmetic operator
Relational operator
Logical operator
Other operators

4.18.1. Arithmetic operator #

The following table lists the common arithmetic operators in the Lua language, setting A to 10 and B to 20:

Operator	Description	Example
`+`	Addition	A + B output result 30
`-`	Subtraction	A-B output result-10
`*`	Multiplication	A * B output result 200
`/`	Division	B / A output result 2
`%`	Take the remainder	B An output result 0
`^`	Multiplying power	A^2 output result 100
`-`	Minus sign	-A output result-10
`//`	Integer division operator (> = lua5.3)	5Compact 2 output result 2

4.18.2. Example #

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

Example #

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

The execution results of the above procedures are as follows:

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

In lua, / is used as a division operation, the result contains the decimal part, // is used as an integral division operation, and the result does notinclude the decimal part:

Example #

a = 5
b = 2
print("The value of division operation - a/b is ", a / b )
print("The value of integer division - a/b is ", a // b )

The execution results of the above procedures are as follows:

Division operation - the value of a/b is 2.5
The value of integer division - a/b is 2

4.18.3. Relational operator #

The following table lists the common relational operators in the Lua language, setting the value of A to 10 and the value of B to 20:

Operator	Description	Example
==	Equals, checks whether two values are equal, returns true, otherwise returnsfalse	(A == B) is false.
~=	Not equal. Check whether two values are equal. Return true if they are not equal, otherwise return false.	(A ~= B) is true.
>	Greater than, if the value on the left is greater than the value on the right, return true, otherwise return false	(A > B) is false.
<	Less than, if the value on the left is greater than the value on the right, return false, otherwise return true	(A < B) is true.
>=	Greater than or equal to, if the value on the left is greater than or equal to the value on the right, return true, otherwise return false	(A >= B) returns false.
<=	Less than or equal to, if the value on the left is less than or equal to thevalue on the right, return true, otherwise return false	(A <= B) returns true.

4.18.4. Example #

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

Example #

a = 21
b = 10
if( a == b )
then
   print("Line 1 - a = b" )
else
   print("Line 1 - a ≠ b" )
end
if( a ~= b )
then
   print("Line 2 - a ≠ b" )
else
   print("Line 2 - a = b" )
end
if ( a < b )
then
   print("Line 3 - a < b" )
else
   print("Line 3 - a ≥ b" )
end
if ( a > b )
then
   print("Line 4 - a > b" )
else
   print("Line 5 - a ≤ b" )
end
-- Modify the values of a and b
a = 5
b = 20
if ( a <= b )
then
   print("Line 5 - a ≤  b" )
end
if ( b >= a )
then
   print("Line 6 - b ≥ a" )
end

The execution results of the above procedures are as follows:

Line 1 - a ≠ b
Line 2 - a ≠ b
Line 3 - a ≥ b
Line 4 - a > b
Line 5 - a ≤  b
Line 6 - b ≥ a

4.18.5. Logical operator #

The following table lists the common logical operators in the Lua language, setting the value of A to true , the value of B is false :

Operator	Description	Example
and	Logic and operators. If A is false, return A, otherwise return B.	(A and B) is false.
or	Logic or operator. If A is true, return A, otherwise return B.	(A or B) is true.
not	Logical non-operator. Contrary to the logic operation result, if the condition is true, the logic is not false.	not (A and B) is true.

4.18.6. Example #

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

Example #

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("---------Divider---------" )
-- 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 execution results of the above procedures are as follows:

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

4.18.7. Other operators #

The following table lists the concatenation operators in the Lua language and operators that calculate the length of a table or string:

Operator	Description	Example
	Concatenate two strings	a..b, where an is “Hello”, b is “World”, and the output is “Hello World”.
#	Unary operator that returns the length of a string or table.	#”Hello” returns 5

4.18.8. Example #

We can better understand the application of concatenation operators and operators that calculate the length of tables or strings through the following examples:

Example #

a = "Hello "
b = "World"
print("Connection strings a and b ", a..b )
print("B String length ",#b )
print("String Test Length ",#"Test" )
print("Newbie tutorial website length ",#"www.runoob.com" )

The execution results of the above procedures are as follows:

Connection strings a and b    Hello World
B String length     5
String Test Length     4
Newbie tutorial website length     14

4.18.9. Operator precedence #

The order from high to low:

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

Except ^ and .. all binary operators outside are left concatenated.

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

4.18.10. Example #

We can get a more thorough understanding of the precedence of Lua language operators through the following examples:

Example #

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

The execution results of the above procedures are as follows:

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