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<h2>Advanced features of OEF</h2>

<h3>Hiding image names</h3>

If your exercise requires recognition of a randomly picked picture, the file

name of the picture might give clue to the exercise. In order to hide this

file name, you can write in parts

<span class="tt wims_code_variable">statement</span>,

<span class="tt wims_code_variable">feedback</span>, etc

<pre>\img{\imagedir/picture.jpg alt="picture"}</pre>

Then on the browser, the student will see

<pre>&lt;img src="a_random_unrelated_file_name" alt="picture" /&gt;</pre>

The true file name is thus hidden to the student.

<p><b>Note</b>. Do not use directly the WIMS command <span class="tt wims_code_words">rename</span> to

process the file name, or the exercise would not work correctly under saved

environment.

</p>

<h3>Multi-step exercises</h3>

Multi-step exercises can be defined via the command <span class="tt wims_code_variable">\steps</span>. For

example, if you define (among parameters)

<pre>\steps{choice 1, reply 1

choice 2, reply 2, reply 3

choice 3

}</pre>

<p>

the exercise will be presented with 3 steps, the first asks for a multiple

choice (choice 1) and a freestyle reply (reply 1), the second a multiple

choice and two freestyle replies, etc.

</p><p>

The content of <span class="tt wims_code_variable">\steps</span> accepts (earlier-defined) parameters as well as

conditional definitions, in the same way as the definition of parameters.

This allows you to selectively present response

fields (according to random variations of parameters), even in the case

where there is only one step.

</p><p>

It is to be noted that if a user makes a mistake in

an early step, subsequent steps will not be presented (and will be

considered all wrong).

</p><p>

The current step number is available to the statement of the exercise,

via the variable

<span class="tt wims_code_variable">\step</span> which takes successively the values of 1,2,... when the user

advances in his/her answering.

</p><p>

To make dynamic multi-step exercises (steps varying with student answers), you

can use the command <span class="tt wims_code_words">\nextstep{...}</span>. The content of

<span class="tt wims_code_variable">\nextstep</span> is the similar to <span class="tt wims_code_variable">\steps</span> but only the first line

is effective. It is useful only when the content is given by a variable

which is changed by post-reply parameter definitions. The exercise stops when

the content of <span class="tt wims_code_variable">\nextstep</span> is empty at some step.

</p><p>

In any case, at most one declaration <span class="tt wims_code_variable">\steps</span> or <span class="tt wims_code_variable">\nextstep</span>

should appear in an OEF source.

</p>

<h3>Conditional branching and loops</h3>

Available commands:

<pre>

\if{condition}{if_content}

\if{condition}{if_content}{otherwise_content}

\ifval{condition}{if_content}

\ifval{condition}{if_content}{otherwise_content}

\for{var=n1 to n2}{loop_content}

\while{condition}{loop_content}     (main environment only)

</pre>

These commands can be used either within statement, hint, solution or

feedback, or in the main environment. In the latter case, the conditional

execution only affects parameter definitions.

<h3>Preprocessed sources</h3>

This feature is not available for Createxo. You can use it if you write OEF

(and Deductio) exercises under Modtool.

<p>

It allows you to include common portions of codes into several oef files.

You can also use it to make batch generation of several oefs from one

pre-source, each differing from the others by some macro definitions.

</p><p>

To use this feature, a subdirectory cpp/ should be created under src. Put

into it pre-source files with extension .cpp. In these files, you can add

cpp directives like <span class="tt wims_code_words">#include</span>, <span class="tt wims_code_words">#define</span>

or <span class="tt wims_code_words">#if</span>.

(Please refer to cpp

manual and c specification for details of the syntax.)

</p><p>

The first line of the cpp file must define a list of targets, in the format

</p>

<pre>

target=targ1 targ2 targ3 ...

</pre>

This line means that this cpp file should generate targ1.oef, targ2.oef, etc.

(the extension .oef will be

appended to the output names). When generating the target file <em>targ1</em>, a macro

<em>TARGET_targ1</em> is defined.

Therefore in the cpp source file, you can add lines like

<pre>

#if defined TARGET_targ1

 \title{Exercise 1}

 \integer{v1=3}

 \text{t1=this is target 1}

#endif

#if defined TARGET_targ2

 \title{Exercise 2}

 \integer{v1=5}

 \text{t1=this is target 2}

#endif

</pre>

in order to make the contents target-dependent.

<p>

The name of the file (in the example,

<span class="tt wims_code_words">targ1</span>, ...)

is available by the variable

<span class="tt wims_code_words">OEFFILE</span>.

In the following example, the title of the exercise will be

<span class="tt wims_code_words">targ1</span>

</p>

<pre>

#if defined TARGET_targ1

 \title{OEFFILE}

 \integer{v1=3}

 \text{t1=dit is target 1}

#endif

</pre>

<p>

Include files should also be put into the src/cpp directory, with extension

.inc. A line

</p>

<pre>

#include "common.inc"

</pre>

will insert the content of common.inc into the generated oef file.

Please note that for security reasons, it is prohibited to specify

directories of include files.

<p>

A special remark: cpp gets confused when your file contains single or double

quotes in the text that are not closed. In this case, you can protect the

commands containing such texts by c comments (<span class="tt">/* ... */</span>).

</p>

<div class="wims_warning">

<span class="wims_warning">$wims_name_warning</span> : In the commands beginning by # as in

<span class="tt">#include</span>, the character <span class="tt">#</span> must be the

first character of the line. You must not

use <span class="tt">#</span> as a character comment.

</div>

<h3>Exercise environment</h3>

A special variable <span class="tt wims_code_variable">\oefenv</span> can be used to test the environment of

an exercise (if it is not redefined within the exercise).

<p>

For the time being, the only testable content of the variable is the word

``debug''. This word appears within <span class="tt wims_code_variable">\oefenv</span> in the following

situations:

</p><ol>

<li>When it is executed within Createxo.</li>

<li>When it is under test in Modtool, by the developer himself.</li>

<li>When it is a class exercise and is executed by the supervisor.</li>

</ol>

<p>Note that in these cases, the good reply will appear as default in the input

fields of many types, allowing you to see what the exercise expects without

typing into the fields.

</p><p>

You may add debugging informations into your exercise using things like

</p>

<pre>

\if{debug iswordof \oefenv}{debugging informations to add into}

</pre>

These debugging informations will be automatically shown when the exercise

is under test, and automatically hidden when students work on it.