Online C++ Code Editor for Interviews

A C++ interview in a shared editor: the candidate writes and compiles code, and you see the edits, compile errors, and output in real time. Suited for systems, game, and back-end interviews. Free, no sign-up, no compiler install.

Free, no sign-up

Code sample

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> v = {5, 1, 4, 2, 3};
    std::sort(v.begin(), v.end());
    for (int x : v) std::cout << x << ' ';
    std::cout << '\n';
    return 0;
}

Output

1 2 3 4 5

What the editor does

  • GCC 10.2: the code compiles and runs on the server in an isolated sandbox, and every participant sees compile errors and output.
  • Real-time collaborative editing: up to 5 participants, with edits and cursors visible instantly.
  • The problem statement is written in Markdown right in the session, next to the code.
  • The standard library is at hand: containers, algorithms, strings, smart pointers, and I/O streams.
  • After a free sign-in: a task bank, an interview mode with timers, candidate scoring, and interview history.

How to run the interview

  1. Click "Open the C++ editor" — the session is created with a sample program, which you can replace with your own task.
  2. Describe the problem in Markdown and send the link to the candidate: they need no sign-up.
  3. Have the candidate verify the solution right from main — for example, call the function on a few inputs and print the result. You will see compile errors and output together with them.

Typical interview tasks

  • Implement a simplified smart pointer like unique_ptr and explain the RAII idiom: who releases the resource, and when.
  • Write a move constructor and move-assignment operator for a class with a dynamic buffer, and explain when they are called.
  • Binary search without overflow when computing the midpoint: why (l + r) / 2 is dangerous, and how to fix it.
  • An LRU cache on std::list and std::unordered_map with get and put in O(1).
  • Reverse a singly linked list in place, with no extra memory.
  • Two pointers on a sorted array: find a pair with a given sum in linear time.

Limitations

  • There are no autotests for C++ yet — verify the solution with calls and output from main.
  • No keyboard input: std::cin receives no data — provide it in the code.
  • Compilation is limited to 10 seconds, and a run to 3 seconds and 64 KB of output.

FAQ

Which compiler is used?
GCC 10.2. The code compiles and runs on the server, so the result is the same for every participant.
Are there autotests for C++?
Not yet. The solution is verified with calls from main and output — this also shows how the candidate tests their own code.
Can I use third-party libraries?
No, only the standard library is available — it is enough for interview tasks.
Can the solution span multiple files?
No, the solution is written in a single file. Declare helper functions and classes above main — that is enough for interview tasks.
Do I need to sign up?
No. Create a session, send the link, and start. Signing in is only needed for the task bank, interview mode, and history.

Editors for other languages