DMDX Help.

Set Counter Keyword

<SetCounter designator = expression>
<set designator = expression>

counter designators:

deprecated usages:
<SetCounter N1,N2>
<set N1,N2>
<SetCounter N,
<set N,

      Keyword to define and manipulate either named counters (as of DMDX or classic numbered counters.  For a discussion on the uses of counters see the Simple Counter and the More Complex Counter sections in the built in introduction, not to mention the Indexed Branching and the following dynamic keyword section.

      Preferred usage evaluates
expression using a modified and significantly expanded version of CALC.C that Bob Brodt wrote in 1985 and assigns the result to the specified counter, either the named counter .name. or the numbered one N (or N1 depending on your usage).  If a named counter has been used a negative counter number will be automatically assigned (starting from -1) for internal uses where the name can't be used, the DMDX user however should not need to ever use it.   First deprecated usage sets Counter N1 to value N2, second deprecated usage sets counter N to some value depending on the token string text (see below for a list of tokens).   Counters are used to control branching in DMDX, more specifically for building looping mechanisms but their use extends far beyond that.   Before a counter can be used it must be set up at least once with a <SetCounter> keyword, after that it can be incremented or decremented, conditionally incremented or decremented depending on the subject's response, used as a parameter to control other keywords, tested against with the Branching keywords or set to another value with <SetCounter> again.   Counter values are signed 32 bit integers, if you need to represent real values (for positioning display elements on the screen for instance) then the <macro fxpset> keyword can be used to simulate fixed point arithmetic.     Maximum name length (including dots) is 40 characters and the names are case insensitive and counter namespace is independent from macro namespace so you can quite happily have both a counter and macro with the same name that don't interfere with each other in any way.

    A counter's value can be incremented or decremented with <inc> and <dec>, conditionally incremented or decremented depending on the subject's response with <incic>, <inciw>, <incinr>, <decic>, <deciw> or <decinr> (see the Branching keywords for a full list of possibilities), used as the time out, output to other devices, used to set macros up (particularly handy for uses where DMDX's syntax doesn't otherwise allow the use of a counter), or stored in the output data file with
<EmitCounter>.  Counters can be displayed with <AppendCounter>. (not recommended) or the <sprintf> keyword (recommended).  A counter's value can also be used to set the frame duration with <CounterFrameDuration> or used in looking time studies.

    Possible tokens in
expression and values for text are: The value of counter .name., for example <set counter.newcounter. = counter.oldcounter.> would set (and create if necessary) counter .newcounter. to the value counter .oldcounter. had when this keyword is parsed. Synonym for
CounterN The value of counter N, for example <set counter3 = counter2> would set (and create if necessary) counter 3 to the value counter 2 had when this keyword is parsed.
cN Synonym for CounterN
LastRT Absolute value of the last Reaction Time gathered in whole milliseconds (rounded down).   Because expressions are evaluated as the item is parsed this RT is the previous item's RT, not the RT that might be gathered by the item the expression is in.
LastXT Last Reaction Time (previous item) gathered in whole milliseconds (rounded down).   This will be negative if the response was incorrect.
ErrorRate The error rate at the end of the previous item (useful for multiple tests against the error rate as a branch on the error rate will reset it).  There's an example of how to display the error rate in the <apc> documentation.
ClockOnTime The millisecond time that the clock was last turned on.  This has two possible values depending on whether <RecordClockOnTime> is turned on.  If <rcot> is on then loading a counter with clockontime will return the time the most recent clock on occurred since the first clock on in the item file, otherwise it is the time since the item file commenced execution.
MillisecTime The millisecond time when the expression is evaluated (usually the time the item is parsed but it can be later with <AbortItemExpression>) since the item file commenced execution.
VideoTime The current video retrace count when the expression is evaluated since the item file commenced execution.
VideoModeX The current video mode width in pixels.
VideoModeY The current video mode height in pixels.
atoizilliontext The integer value of the previous item's text string entered with <ZillionTypedResponses>.
jobstatus The value of the job status variable that tracks the job state at the time of parsing.  Only useful for the  <AbortItemExpression>.

    Rules regarding evaluation of expression are as follows:

* Calculator program - 9 May 1985
*     Bob Brodt
*     34 Mehrhof Rd.
*     Little Ferry, NJ 07643
*     (201)-641-9582
* This is a simple integer arithmetic calculator program. It uses infix
* notation, i.e. 1+2*3 as opposed to "reverse polish" notation: 1 2 3 * +.
*     Numbers may be input as in C using 0x notation for hex, and a
*     leading zero for octal, everything else is assumed to be decimal.
      Single character constants can be used in single quotes, reserved
      DMDX ones will throw syntax errors if used (for example '"', '>',
      '$' and ';'), there are no escape sequences for non-printing
      characters (' is legal as in ''').
*     DMDX constants at time of evaluation:
*     DMDX counters referenced by,, counterN or cN
*     The following operators are supported (from highest precedence to lowest):
*     ( )                   associativity
*     ~ !                   one's complement, logical NOT
*     * / %                 multiply, divide and modulo
*     + -                   unary and binary add & subtract (note unary operators have problems until, see PROBLEMS below)
*     .SHL. .SHR.           shift left and right
*     .LT. .GT. .LE. .GE.   less than, greater than, less than or equal to and greater than or equal to
*     .EQ. .NE.             equal to and not equal to
*     &                     bitwise AND
*     ^                     bitwise exclusive OR
*     |                     bitwise inclusive OR
*     .AND.                 logical AND
*     .OR.                  logical OR
*     =                     assignment
*     ,                     comma - separates function arguments
*     All operators associate from left to right with the exception of
*     the assignment (=) operator.   Logical operations resolve to 1 if true and 0
*     if false.
*     The calculator also has built-in function capabilities:
*     max(a, b) - larger of a or b
*     min(a, b) - smaller of a or b
*     abs(a) - absolute value of a
*     random(a) - random number between 0 and a-1
*  Precedence of functions is a little weird, currently random(a) + b evaluates to random(a + b) because
*  function call brackets are just brackets, so random a + b is valid syntax with + having the higher
*  precedence.  So the safe use of functions is currently (random a) + b.
*  Similar kind of thing for unary operators -5 + 15 evaluated to -20, eek.  Worse -5 .ge. 0 evaluates to
*  -1 instead of 0.  So you had to have (-5) + 15 and (-5) .ge. 0.  Brute forced a fix in

    Typical use of a counter involves setting it to some initial value and decrementing it and using one of the counter branching keywords <bicGT> till the counter reaches 0.   In the following item 10 will be displayed five times:

0 "looping demo" <set c1 = 5>;
+10 * "display"
<dec 1> <bicGT 1,0,-10>;
0 "end";

    Using the named counters and <BranchIf> that looping example might be written as:

0 "looping demo" <set c.loopcounter. = 5>;
+10 * "display" <dec c.loopcounter.> <bi -10, c.loopcounter. .gt. 0>;
0 "end";

    Possible things to be aware of are that expressions (both in <SetCounter> and <BranchIf> keywords), non conditional arithmetic (<inc> and <dec>) and most other actions in counter related keywords are performed as the item is parsed before display so multiple uses of those keywords in the same item are possible.   Whereas conditional arithmetic keywords (<incic>, <inciw>, <incinr>, <decic>, <deciw> or <decinr>) are evaluated after the item is displayed and the RT gathered (thus necessitating special control structures within DMDX) and are limited to one operation per counter per item, in the case of multiple uses only the last will have any effect.   Branches other than <BranchIf> (<bicGT> and <bicLE>) are evaluated at the beginning of the next item after everything else.

    Another typical use of counters involves tracking multiple error rates and branching if the error rates are too high.  In the following each class of test needs an 80% or higher success rate:

100 "start" <set c.test1correct.=0> <set c.test1total.=0>

            <set c.test2correct.=0> <set c.test2total.=0>

            <set c.test3correct.=0> <set c.test3total.=0>;


+1000 "class 1 test" * <incic c.test1correct.> <inc c.test1total.>;

+2000 "class 2 test" * <incic c.test2correct.> <inc c.test2total.>;

+3000 "class 3 test" * <incic c.test3correct.> <inc c.test3total.>;

! repeat items 1000, 2000 and 3000 as needed;


~200 <emit c.test1correct.> <emit c.test1total.>

     <emit c.test2correct.> <emit c.test2total.>

     <emit c.test3correct.> <emit c.test3total.>

  <bi 1000, (c.test1correct. * 100 / c.test1total. .lt. 80) .or.

                 (c.test2correct. * 100 / c.test2total. .lt. 80) .or.

                 (c.test3correct. * 100 / c.test3total. .lt. 80)>;


0 "end";

    See the <ZillionTypedResponses> keyword for a fairly complex counter using example.

    You can manipulate a series of counters as an array using macro indexes.  For example you could have 100 counters between 100 and 199 and access them as a two dimensional 10x10 array using two macros X and Y to access any given element with c1~X~Y for example after using <macro set X=2> and <macro set Y=7> to access element (2,7) (note we're accessing dimensions with indexes from 0 through 9).  If you require more than a dimension of 10 then you more or less have to calculate the index yourself, say you want a one dimensional array and your counters start at 100 and you want to access the element in counter .index. you would need to set a macro to 100 plus your index with <macro set .offset. = c.index. + 100> and then access the element itself with c~.offset. (with the traditional caveat that you have to set your macro up in a different item from the one that evaluates the array element because macros are expanded before the item is parsed).  Alternatively with a bit more gerfingerpoken you can put a leading zero on the index (unless of course you used counters from zero on up) with the <macro fxpset> option used to put leading zeros on macros to be used to position screen elements and discarding the leading zero and decimal point.  For example say you had a one thousand element array stored in counters 1000 through 1999 to access any given element with counter .index. you would have to first set macro X to the ASCII representation of c.index.with <macro fxpset 3 X = c.index.> (if c.index. had the value 7 macro X would wind up with the five characters 0.007) and then discard the leading 0 and decimal point with <macro pop X, c1> <macro pop X, c1> (discarding the 0 and . values into counter 1) allowing you finally access your element with c1~X.


DMDX Index.