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Learn. Practice. Master.Free online compiler, code visualizer and CSE courses

Run Python, C, C++, Java and JavaScript online, watch every variable, call and output step by step, and learn with free CSE courses and exercises with solutions.

Explore courses →▶ Run code online
  • 348 Lessons
  • 732 Practice problems
  • 7 Languages

A real program, running here. Watch each line change the values.

Start your learning journey with a step-by-step course.

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Beginner

Python Programming

From your first print() to classes, recursion and data structures.

40 lessonsBeginner

C++ Programming

C++ from your first cout to references, strings, vectors, the standard library, templates and error handling, with every variable and object on screen.

16 lessonsIntermediate

Data Structures

Lists, stacks, queues, trees, heaps, hash tables and graphs, built in C node by node, with every pointer drawn.

19 lessonsIntermediate

Algorithms

Searching, sorting, recursion, greedy choices, dynamic programming and graph algorithms, with the cost of each one counted.

18 lessons

Interactive tools

Explore, practice, visualize

Tools that show what your code does, one step at a time.

Explore all tools →
Online compilerWrite, run and test code in 7 languages.Try now →Code visualizerSee how your code runs, line by line.Try now →DSA LabOperate 21 data structures and algorithms.Try now →Practice problemsSharpen your skills with 732 problems.Try now →

Compiler

Write code and run it right here

Python, C, C++, Java, SQL, JavaScript and 8086 assembly, with nothing to install and no sign-up. Pick a language, change the code and press Run.

Open the full compiler →
main.pyPython 3.14 (Pyodide)

Output

Press Run to see the output here.

DSA Lab

Every data structure and algorithm, in motion

Put in your own values and watch each operation happen one step at a time, explained in plain English. No code needed.

All 21 tools →
Sorting visualizerBubble, selection, insertion, Shell, merge, quick, heap, counting and radix sort. Each step lights up the line of code that ran and says why.Watch them sort →Concept explainerPointers, stack and heap memory, recursion trees, SQL joins, TCP/IP and neural networks, drawn and explained.Explore concepts →

Data structures

Sorting and searching

Graphs

Problem-solving techniques

How a lesson works

  1. Read A short lesson explains one idea in plain words.
  2. Try Run the example right in your browser, then change it.
  3. See it run Step through every line and watch the values change.

Online compilers

Code visualizers

Free courses for beginners

Common questions

Is StepVioz free?

Yes. Every course, exercise, compiler and visualizer is free, with no account and no ads.

Which languages can I run online?

The online compiler runs Python, C, C++, Java, JavaScript, SQL and 8086 assembly in your browser, with nothing to install.

What is a code visualizer?

A code visualizer runs your program one line at a time and shows the variables, function calls, memory and output at each step, so you can see why the code does what it does.

Can a complete beginner learn to code here?

Yes. The HTML, CSS, JavaScript, Python, C and C++ courses start from the first program, with examples to run, quizzes, and exercises with solutions.

Learn at your own pace, one step at a time

  • 24 Courses
  • 43 Interactive tools
  • No install Runs in your browser
Start learning free →