Difference between revisions of "Do while"

Latest revision as of 01:12, 22 January 2015

LSL Portal

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

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Footnotes

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

Do while