# Exams in the TeachCenter Exam: STACK *STACK questions can be used in a TeachCenter quiz and offer computer-based assessment for mathematics..* *Published: 2 November 2021 · Updated: 3 September 2025* STACK questions and answers **contain mathematical expressions**. Stack evaluates the mathematical expressions entered using computer algebra systems. Answers are not just compared with a model answer, but it is also possible to **recognise and give feedback for consequential errors.** It is possible to create randomised questions or multiple choice questions with STACK as well. ## Creating a STACK exam ## Creating an exam and choosing STACK question type [Create a „Quiz“ activity in the TU Graz TeachCenter.](https://telucation.tugraz.at/en/guides/quiz-tc-exam/) Add a question to a „Quiz“activity or to your question bank as usual. Select the question type **STACK** in the pop-up menu and click **Add**.  *Adding a STACK question* ## Entering question and model answer The „Stack“ question interface features numerous settings. However, only the **question** **name**, the **question text** (which students see), a **model answer at Input:ans1** and a **test for correctness** are mandatory. - **Question name**: give the question a title. - **Question** **variables**: Here you can define variables that will be used in the task, such as in a test answer (in the screenshot: variables „p“, „ta“ and „tac“).  - **Question text**: Enter the assignment here which students will see later. **Do not delete the** **tags** **\[\[input:ans1\]\] \[\[validation:ans1\]\]**. **However, you can replace** **„****ans1****„** **with a** **name of your choice.** You can also use previously defined variables (in the screenshot: {@p@} was previously defined as p:sin(2\*x)). Please note: Use the text-only editor for this. You can change the editor in your profile.  - \[\[input:ans1\]\] is later displayed as a box in which students can enter their answers. \[\[validation:ans1\]\] stands for the feedback on the input, e.g. missing brackets. \[\[feedback:ans1\]\] stands for the feedback from the response tree that appears later, e.g. feedback on the calculation path or the result. These tags can be inserted anywhere in the question text. *Use (..) and \[..\] as the format for inline formulas and mathematical expressions instead of $..$ and $$..$$ as in LaTeX.* - A question can also demand several inputs. To do this, insert further inputs and feedback fields with a different name at the appropriate place, e.g. \[\[input:ans2\]\]. - **Input:ans1 (the name of the section changes depending on the variable name)** **–** Click on this section to expand it. Enter at least a model solution in the corresponding field, either written out in full or as a previously defined variable (here: „ta“). - Maxima syntax must also be used for the model solution instead of LaTeX syntax. You will find more information on correct input [in the STACK documentation in the Answer Input section.](https://github.com/maths/moodle-qtype_stack/blob/master/doc/en/Students/Answer_input.md) - Different input types can be selected for the model solution. The default is algebraic input. - If the question requires several inputs, a model answer must be defined for each input.  - **Respons****e** **tree:** The response tree is used to decide whether the students‘ answer is correct. By default, there is a response tree with a response node for each input. - The students‘ answer (SAns) is compared with the teacher’s answer or model answer (TAns). If they match (=AlgEquiv at answer test), the TRUE node is executed. If they do not match, the FALSE node is executed.  - In each node, points (**score**) or **penalties** can be given based on the answer. In addition, textual **feedback** for students can be stored in each node. For more complex answers, it is possible to select where to continue in the tree or that the response tree ends here (=\[**stop**\]). An answer hint can also be given. - Save the questions by clicking **Save** **changes** and continue editing at the bottom of the page. **Please note****: Before students complete the quiz, you should** **test** **your questions. You also need to generate answer variants for questions if they contain random variables.** In the next step, we describe how this works. ## Previewing and testing questions - Click **Preview** next to the **„****Save** **changes and continue editing****“** button to see a preview.  - At the top right, there is an information that **question tests or variants are missing**. Click on it.  - To add a test case for a **question without randomised variables**, click **Add** **a t****est** **c****ase** and fill in the input and expected answer. Please note: Only the result is checked, not the calculation.  We recommend writing several test cases, e.g. correct answer, wrong answer and any common mistakes students might make. ## Adding tests and variants for questions with randomised variables If your question contains random variables, you have the option to pre-generate and save „**variants**„. Students will then receive one of these options. By testing variants, you can rest assured that the values students will receive actually work, are of the **same difficulty** or that they **do not contain any values that have exceptions** associated with them. The use of pre-generated variants **reduces the server load during a test**. If no variants are saved, students will receive completely randomised variables. - Open the question preview. At the top right, you will see an information that **tests or variants are missing**. Click on it. - Tragen Sie bei **# Varianten bereitstellen** die gewünschte Zahl and Zufallsvariablen ein und klicken Sie auf den Button. Hinweis: STACK bricht das Hinzufügen von Varianten ab, wenn ein Test fehlschlägt.  - Insert the number of variants you want to deploy next to **Deploy # of variants** and click on the button. Please note: STACK will stop adding variants if a test fails.  ## During and after a STACK exam ## Student Input - Students find STACK questions, like other question types, **in a quiz in the TeachCenter (Exam)**. - Students **enter their answers using mathematical expressions**. STACK interprets the input and displays how the input was interpreted. Students must **confirm their input again**. - Students receive the feedback stored in the feedback tree and the corresponding points. ## Grading STACK questions - Questions on Stack are assessed by the **response tree**. The points are awarded just like for any other question type in the TeachCenter, and can be found in the overall grade of the quiz. - To see more detailed results, switch to the **Results tab** in the quiz, just like with other question types. For more information on grading a quiz in the TeachCenter, [see the manual „Grading“](https://telucation.tugraz.at/en/guides/grading-tc-exam/) ## Help & contact For further help, please read the [official Moodle documentation on STACK](https://docs.moodle.org/405/en/STACK_question_type) and the [STACK documentation on GitHub](https://github.com/maths/moodle-qtype_stack). More information for students in the [Student Guide](https://github.com/maths/moodle-qtype_stack/blob/master/doc/en/Students/Answer_input.md). To see an example quiz with STACK questions, please go to [the public TeachCenter course „Test Your Exam“](https://exam.tugraz.at/moodle/course/view.php?id=267). We recommend hosting a mock exam with students so they can familiarise themselves with the question type. For questions on TeachCenter / TeachCenter Exam: [tc@tugraz.at](mailto:tc@tugraz.at)