View source for If

{{#vardefine:p__desc|
}}{{#vardefine:p_condition_desc|If this executes as true then '''branch''' is executed.
}}{{#vardefine:p_condition_d_desc| If this executes as true then '''branch_true''' is executed otherwise '''branch_false''' is executed. 	
}}{{#vardefine:p_branch_desc|Can be either a single statement, a block statement, or a null statement.
}}{{LSL_Conditional
|statement=if
|p1_name=condition
|p2_name=branch
|statement_header
|statement_desc
|statement_title=if ( {{LSL Param|condition}} ) {{LSL Param|branch}}
|extras=
<div id="box">
== if ( {{LSL Param|condition_d|condition}} ) {{LSL Param|branch|branch_true}} else {{LSL Param|branch|branch_false}} ==
<div style="padding: 0.5em;">
{{{!}}
{{LSL DefineRow||condition|{{#var:p_condition_d_desc}}}}
{{LSL DefineRow||branch_true|{{#var:p_branch_desc}}}}
{{LSL DefineRow||branch_false|{{#var:p_branch_desc}}}}
{{!}}}

There seems to be no limit anymore (or very high > 120) for else-if chains.
</div>
</div>
|spec=Operators in LSL do NOT [http://en.wikipedia.org/wiki/Short-circuit_evaluation short circuit]. For example:
{{{!}} style="border-width: 0px;border-spacing: 0px;"
{{!}}<lsl>// A simple method to say if the method was called.
integer test()
{
    llOwnerSay("Test method called!");
    return TRUE;
}

default
{
    touch_start(integer total_number)
    {
        if (FALSE && test())
        { // If short-circuit optimized then the test() should never be called.
          // Will never get here.
        }
    }
}</lsl>
{{!}}}
In a short-circuited language if the left-hand side of a logical AND (&&) is FALSE the right-hand side is never tested since the entire test would always return a FALSE output no matter what the value of the right-hand side. Since LSL is not short circuited, both the left and the right-hand sides are tested all the time.
This can be simulated by using a nested if structure:

<lsl>default
{
    touch_start(integer total_number)
    {
        if (FALSE)
        {
            if (test())
            {
              // Will never get here.
            }
        }
    }
}</lsl>
|examples=Simple inline if statement:
<lsl>if (a == 1) c = b;</lsl>

Simple block if statement:
<lsl>if (a == 1)
{
    // Do something here.
}</lsl>

Complex if/else block (only one line of text will be said by this example)
<lsl>if (a == "Loren") {
    llSay(0, "Lorem ipsum sic amet!");
} else if (a == "Bob") {
    llSay(0, "Babble dabble rabble rouse.");
} else {
    llSay(0, "Gobbledygook?  or English?");
}</lsl>

Compounded if statement:
<lsl>if (a == 1 && b == c)
{
    // more here.
}</lsl>

Nested if statements:
<lsl>if (a == 1)
{
    if (b == c)
    {
        // more here.
    }
}</lsl>

Watch out for misplaced semicolons.  They can, and will, cause strange things to happen.
For instance: If you place a semicolon between an if statement and a code block, the if statement will not control the execution of the block.
<lsl>if (a == "Loren");
{
    llSay(0, "Lorem ipsum sic amet!");
}</lsl>

This code will execute in the following order:

# The line <code>if (a == "Loren");</code> will execute; the semicolon will tell LSL that this is a simple inline if statement.
# Next it meets the start of the code block and will execute the contents, in this case saying "Lorem ipsum sic amet!", no matter what the outcome of the above if statement.

Another problem happens when someone forgets to use the curly braces.
<lsl>if (a == "Loren")
    llSay(0, "Lorem ipsum sic amet!");
    llSay(0, "I don't know what it means either...");</lsl>

The assumption is that because the indentation makes it "look" like both llSay commands are controlled by the if statement, that they are.  In fact, if <code>a</code> was equal to "Joe" then all that would be said is "I don't know what it means either..."

There is common error to mistake  == operator for =, due to  ignorance or simply mistyping, e.g.

<lsl> 
if (av_id = llGetOwner())
         llSay("It's my owner!");<lsl>
will send message regardles what value of va_id was , because it equal to if(llGetOwner()).
 
There is trick , invented by C programmers ages ago how to avoid this bug  -  to make habit to put constant or other expression to which you cannot assign value(e.g. function call or  result of some operation) in front of comparison - that will save you from mistake. It's very nasty error to make and hard to debug in big code.

<lsl> 
if(llGetOwner() == av_id)
          llSay("It's my owner!");<lsl>

In this case mistake will result in compile error.

|helpers
|also_header
|also_functions
|also_tests
|also_articles
|also_footer
|notes
|mode
|deprecated
|cat1=Conditional
|cat2
|cat3
|cat4
}}