Do while

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/LSL

do while

do loop while (condition);

•	loop	–	Executes once, then executes condition.
•	condition	–	If condition executes true, it then loops back and executes loop again.

Any of the statements can be null statements. A do...while loop is slightly faster than a while or for loop, and requires fewer bytes of memory than a while or for loop. (However, the speed increase and byte difference does not apply to scripts compiled in Mono)

Specification

Conditional Types

Type	Condition
integer	True if it is not zero.
float	True if it is not zero.[1]
string	True if its length is not zero.
key	True only if it is a valid key and not NULL_KEY.
vector	True if the vector is not ZERO_VECTOR.
rotation	True if the rotation is not ZERO_ROTATION.
list	True if the length is not zero. Note that correct behavior is only seen with Mono-compiled scripts; LSO-compiled scripts incorrectly resolve to false if the list is non-empty: BUG-230728

Examples

//Counts from 1 to 5
default
{
    state_entry()
    {
        integer olf;   // Without applied value an integer will be defaulted to zero.
        do
            llSay(0, (string) (++olf));       // Increment before the while condition 
        while (olf < 5);                    // On the first pass/loop olf = 1
    }
}

//Counts from 0 to 4
default
{
    state_entry()
    {
        integer olf;
        do
            llSay(0, (string)olf);    // olf is still equal to zero at first iteration
        while (++olf < 5);            // Increments then does the while-test
    }
}

//Counts from 0 to 4 and comments as it loops (block statement demo)
default
{
    state_entry()
    {
        integer olf;
        do
        {   // Curly brackets are required since there is more than one statement within the do-loop
            llSay(0, (string)olf);    
            llSay(0, "looping");
        }
        while (++olf < 5);
    }
}

//Practical example of where a do/while loop is more immediately useful than a while loop:
//Note that a sensor event always contains input data, so the 'do' always has something to process
    sensor(integer num)
    {   
        if (num > 12)
            num = 12;
        do
        {   
            // --num decrements num before using it to pick up a detected avatar's name. Thus we retrieve #11 through #0
            gNameList += [llGetSubString(llDetectedName(--num), 0, 23)];    //sometimes avatar names are too long for dialog display
            gKeyList  += [llDetectedKey(num)];    //we will dialog select avatar by name, but still need their key
                                                  //even if their name has not been truncated above
        }  while (num > 0);
        llDialog(llGetOwner(), "Choose an avatar.", gNameList, gDlgChan);  //channel is pre-defined when llSensor is triggered
    }

Deep Notes

Search JIRA for related Issues

Footnotes

1. ^ The OpenSim LSL compiler will not do this implicitly. You will need to use an explicit check.

Do while