Skills Code problems

Code questions, traced line by line on a teacher’s board.

Paste the code and the question, or drop a photo or PDF of the paper, and Chasca makes a video that walks through the code as the computer runs it: the code stays beside the working, each value is written on the board as it changes, and the output or the fix is boxed. It also works number systems, truth tables and SQL queries, for computer science teachers and course creators, and every answer is worked out a second time before the video is made.

Make a code tracing video Watch the full video

16:9, widescreen
1 minute to 30 minutes
Computer science teachers and course creators

Made from this prompt: “Trace these for my class. 1) What is the output? x = [1, 2, 3] y = x y.append(4) print(len(x)) 2) Convert 45 to binary, then to hexadecimal.”

At a glance

What you get.

Format: 16:9, widescreen
Length: 1 minute to 30 minutes
Starts from: Pasted code and questions, or photos, a PDF or a document of the paper (up to 20 pages)
Languages: All 79 languages for the narration; the code stays exactly as written
Look: A black board or a whiteboard, your code beside the working and the trace written as it is said
Narration: Any of the 30 narrators or your own voice, with captions
Price: Uses your plan’s minutes like any video, from $9.99 a month for 30 minutes. Your first 2 videos are free, up to a minute each.

Who it’s for

Made for people who teach programming.

Computer science teachers

Give each “what does this print?” question on the worksheet a trace students can replay, value by value, the night before the test.

Course creators

Add a worked trace under every exercise in your course, explained in your learners’ language, with the code words said the way programmers say them.

Tutors and mentors

Show a student why a line fails, an index past the end of a list or a missing colon, then the fix, one step at a time.

Why a skill

A general video maker can’t trace code.

Ask a general AI video tool to explain a program and you get a voice over code scrolling past, or a talking avatar. Students learn to trace by watching each variable change, line by line, next to the code. That is the only thing this skill makes.

Your code stays on the board beside the working from the start, copied exactly, indentation included.
It is walked through as the computer runs it, each value said as it changes, and the board writes the trace: “i = 2 → total = 3”.
The line the explanation dwells on is highlighted in the code.
An error gets its line, the reason it fails and the fix; a number-system question gets each division or place value in turn.
Truth tables are filled row by row, and an SQL query shows which rows it keeps and why.
Code words are read the way programmers say them (“plus equals”, “double equals”, “modulo”) and are never translated.
Every answer is worked out a second time from the same code before it is boxed. If the two disagree, the video’s page tells you.

How it works

From a code question to a traced solution.

1
Paste the code and the question

Output questions, finding errors, number systems, truth tables or SQL on a table, typed or as a photo or PDF.
2
Traced line by line

The code sits beside the working and is walked through as the computer runs it, each value as it changes.
3
The trace on the board

Values, outputs and errors are written step by step on the board as they are said.
4
Checked, then boxed

The answer is worked out a second time before it is boxed, and code words are read the way programmers say them.

Examples

Videos made with this skill.

A shared Python list, then 45 in binary and hex
A list two names point to, traced line by line beside the code, then a number converted step by step.
PromptTrace these for my class. 1) What is the output? x = [1, 2, 3] y = x y.append(4) print(len(x)) 2) Convert 45 to binary, then to hexadecimal.
Made from a promptCode problemsEnglish
Converta 45 para binário e hexadecimal
Number systems in Brazilian Portuguese: dividing by two, then grouping the bits into hexadecimal.
PromptConverta 45 para binário e depois para hexadecimal.
Made from a promptCode problemsPortuguese
A truth table for (A AND B) OR NOT C
All eight rows worked out on the board, each half first and then OR, ending with the pattern in the last column.
PromptFill in the truth table for (A AND B) OR NOT C.
Made from a promptCode problemsEnglish
Find the error in two lines of Python
A for loop missing its colon: the error found, why Python stops before printing anything, then the corrected line.
PromptFind the error: for i in range(5) print(i)
Made from a promptCode problemsEnglish
Tracing an SQL query, clause by clause
FROM, WHERE, ORDER BY and SELECT applied in the order SQL runs them, on a small table of students’ marks.
PromptTrace this on students(name, marks) with Asha 92, Ravi 78, Meera 85: SELECT name FROM students WHERE marks > 80 ORDER BY marks DESC;
Made from a promptCode problemsEnglish
¿Qué imprime esta función recursiva?
Recursion explained in Spanish: f(4) unfolded call by call down to the base case, then multiplied back up to 24.
Prompt¿Qué imprime este código? def f(n): return 1 if n == 0 else n * f(n - 1) print(f(4))
Made from a promptCode problemsSpanish

What it won’t do

Run your code on a computer: it is traced, then worked out a second time.
Draw logic gate symbols yet: logic questions are worked with truth tables.
Fit a long program on the board: the code beside the working holds about 15 lines, the length of an exam question.

Why we built it

Tracing is how students learn what code really does, and it is the step they skip when nobody is watching. A teacher can trace one loop at the board, but not every question on every worksheet for every student who missed the lesson. We built the code skill so each question can have its trace, value by value, in the language the class is taught in.

Read why we built it

FAQ

Questions, answered.

Something else? The main FAQ covers voices, languages and the API.

Yes. Chasca’s Code problems skill makes a narrated video that traces your code line by line on a teacher’s board: the code stays beside the working, each value is written as it changes, and the output is boxed. Paste the code and the question, or upload a photo or PDF of the paper.

No. The code is traced the way a teacher traces it, and the answer is worked out a second time from the same code before the video is made. If the two answers differ, the video’s page tells you which question to check.

Output and tracing questions, finding and fixing errors, number systems such as denary to binary or hexadecimal, truth tables, algorithms, recursion and SQL queries on a table. An algorithm can be drawn as a flowchart and a recursion as a tree of its calls.

Paste the code in the language your course uses: it is shown exactly as written and read the way programmers read it. Questions it writes for you are in Python unless you ask for another language.

Yes, in any of the 79 languages Chasca narrates in. The explanation is in your language, while the code, its keywords and its names stay as written and are said the way programmers say them.

From one minute to 30 minutes on a paid plan; the free videos are up to a minute. A video follows its questions, each on its own board, so several questions make a longer video.

Your first 2 videos are free, up to 1 minute each, watermarked. No card required. A skill works on the free videos too, up to a minute. After that, plans start at $9.99 a month for 30 minutes. See pricing.

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Code questions, traced line by line on a teacher’s board.

What you get.