LSL Operators
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Operators are used to cause an operation (or mathematical action) to be performed on one (such as !) or two operands. The easy and common example is 1 + 2 where 1 and 2 are operands, and the + is the operator. This concept can be extended much further with LSL since operands can be variables with the special case of the assignment operators requiring that the left hand side be a variable.
The following table lists the operators in descending order of evaluation, i.e. higher in the table means higher evaluation precedence. Multiple operators on the same line share evaluation precedence. Parenthesize an expression if you need to force an evaluation order.
Operator  Description  Usage Example 

()

parentheses: grouping and evaluation precedence  integer val = a * (b + c);

[]

brackets: list constructor  list lst = [a, 2, "this", 0.01];

(type)

typecasting  string message = "The result is:" + (string)result;

! ~ ++ 

logical NOT, bitwise NOT, increment, decrement  counter++;

* / %

multiply/dot product, divide, modulus/cross product  integer rollover = (count + 1) % 5;



subtraction, negation  integer one = 3  2;

+

addition, string concatenation  integer two = 1 + 1;

+

list concatenation  list myList = [1, 2, 3] + [4, 5];

<< >>

arithmetic left shift, arithmetic right shift  integer eight = 4 << 1;

< <= > >=

less than, less than or equal to, greater than, greater than or equal to  integer isFalse = (6 <= 4);

== !=

comparison: equal, not equal  integer isFalse = ("this" == "that");

&

bitwise AND  integer zero = 4 & 2;

^

bitwise XOR  integer zero = 4 ^ 4;



bitwise OR  integer four = 4  4;

&& 

logical AND, logical OR  integer isFalse = (FALSE && TRUE);

= += = *= /= %=

assignment  integer four = 4;

Note: Unlike most other languages that use the Cstyle &&
and 
operators, both operands are always evaluated. For example,
if (TRUE  1/0) llSay(PUBLIC_CHANNEL, "Aha!");
 will cause a Math Error rather than say "Aha!"
Note: The ++
(increment) and 
(decrement) operators have two versions, pre and post. The preincrement (or predecrement) operator increments (or decrements) its operand by 1; the value of the expression is the incremented (or decremented) value. The postincrement (or postdecrement) operator increases (or decreases) the value of its operand by 1, but the value of the expression is the operand's original value prior to the operation.
integer count = 0;
if( ++count == 1 ) // 'count' is incremented then evaluated.
llSay(PUBLIC_CHANNEL, "Aha"); // message will be said.
integer count = 0;
if( count++ == 1 ) // 'count' is evaluated then incremented.
llSay(PUBLIC_CHANNEL, "Aha"); // message will not be said.
Note: In most programming languages, and in the LSL bitwise operators, the AND operator has greater precedence than the OR operator. However, the LSL logical operators  and && have the same precedence. For example:
1  1 && 0 // result: 0 because it's the same as (1  1) && 0
1  1 & 0 // result: 1 because it's the same as 1  (1 & 0)
Note: The order of evaluation is from right to left. If the value of x starts as 1 then the first two conditions below evaluate false and the second two evaluate true:
(x && (x = 0) == 0 && x)
(x && (x = 0) == 0 && x == 0)
(x == 0 && (x = 0) == 0)
(x == 0 && (x = 0) == 0 && x)
Both sides are evaluated regardless of the the truth of either side.
% Modulus
Note: Modulus (%
), like division, cause a Script runtime error. Math Error when its second operand equals zero.
Note: The %
operator only accepts integer (%
as modulus) and vector (%
as cross product) operands.
The modulus, also known as Modulo, produces the remainder after the first operand is divided by the second. Mathematically a % b
is equivalent to a  (a/b) * b
, since integer division a/b
is truncated. This is also why the second operand cannot be zero.
The operator can be confusing, even to veteran scripters. The following example(s) may prove useful in understanding how modulus can be used:
 Determine if an integer input is even or odd:
if (input % 2 == 0) // input is even
{
// do even things
}
else // it's odd
{
// do odd things
}
 In the LSL implementation, the result always has the same sign as the first operand.
 7 divided by 3 is 2 with a remainder of 1 (3 * 2 = 6, so the difference is 7  6 = 7 + 6 = 1),
7 % 3 == 1
.  Conversely, 7 divided by 3 is 2 with a remainder of 1 (3 * 2 = 6, so the difference is 7  6 = 1),
7 % 3 == 1
.
 7 divided by 3 is 2 with a remainder of 1 (3 * 2 = 6, so the difference is 7  6 = 7 + 6 = 1),
 If the second operand is known to be a positive power of two, the modulus
a % b
can be replaced with the bitwise AND operatora & (b1)
which is more efficient.7 % 4
and7 & 3
are both 3. However, AND always returns a positive value:
7 % 4 == 3
, but7 & 3 == 1
, which is 4 greater than the modulus putting it in the positive. This may or may not be desirable depending on the situation.
 Sometimes taking a modulus of floating point numbers is useful. The formula from the introduction works as long as the quotient is cast to an integer:
a  (integer)(a/b) * b
. Take the fractional part of
a
(b
is 1.0 and can be left out):7.8813  (integer)(7.8813) == 0.8813
.  Limit an angle
a
within TWO_PI radians, i.e. a full circle:7.8813  (integer)(7.8813/TWO_PI) * TWO_PI == 1.598114
.
 Take the fractional part of
+ Operator
Note: Equality test on lists does not compare contents, only the length.
Left Type  Right Type  Result Type  Description 

integer  integer  integer  Adds left and right 
integer  float  float  Adds left and right 
float  integer  float  Adds left and right 
string  string  string  Concatenates right onto the end of left. 
list  *  list  Concatenates right onto the end of left. 
*  list  list  Affixes left onto the start of right. 
vector  vector  vector  Adds left and right 
rotation  rotation  rotation  Adds left and right Not useful for combining rotations, use * or / instead. 
Shorthand Operators
Simple assignment operator  Shorthand operator 

a = a + 1  a += 1 
a = a – 1  a = 1 
a = a * (n+1)  a *= (n+1) 
a = a / (n+1)  a /= (n+1) 
a = a % b  a %= b 
De Morgan's laws
AND  OR 

~(a & b) 
~a  ~b

~a & ~b 
~(a  b)

a & ~b 
~(~a  b)

~(a & ~b) 
~a  b

AND  OR 

!(a && b) 
!a  !b

!a && !b 
!(a  b)

a && !b 
!(!a  b)

!(a && !b) 
!a  b

Due to De Morgan's laws, by row, code in the AND column is logically equivalent to code in the OR. a and b need not be variables, they can be expressions. In certain circumstances these equivalencies can be used to simplify complex code. It is important not to confuse the two sets when using them. The first two rows depict De Morgan's laws as it is formulated, the second two build upon it.
Useful Snippets
Typecasting can also be used if you have to concatenate many parts into a string:
// the following twp statements are equivalent:
string message1 = (string)["I have ", 5, " children at the average age of ", 8.2, " years"];
string message2 = "I have 5 children at the average age of 8.200000 years";