Online C++ Compiler — Numio

Compile and run C++20 code online with Clang in your browser. iostream, STL, cin input and clear compile errors. Free, no sign-up, nothing uploaded.

Runs in your browser · No sign-up

Code (C++)

Ctrl/⌘ + Enter to run

Program input (stdin)

input() and io.read() read these lines in order.

Output

Code runs locally in your browser; it is not uploaded.

How to use

Write or paste C++ code with a main function.
Optional: type input for std::cin in the input box.
Press Run (or Ctrl/⌘ + Enter) to compile and run.

Example

// C++ example
#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> nums = {3, 1, 4, 1, 5, 9};
    std::sort(nums.begin(), nums.end());

    std::cout << "Sorted:";
    for (int n : nums) {
        std::cout << ' ' << n;
    }
    std::cout << "\nMax: " << *std::max_element(nums.begin(), nums.end()) << '\n';
    return 0;
}

Details and limitations

Code is compiled to a WebAssembly (WASI) program by Clang, itself running as WebAssembly. The toolchain (about 25 MB) downloads on first use and is cached afterwards.

Compiling C++ usually takes several seconds and does not count toward the 10-second run limit. Programs are 32-bit, threads are not available and exceptions are not supported.

FAQ

Which C++ standard is supported?

C++20, including iostream, std::string and STL containers and algorithms such as vector, map and sort.

How do I read input with cin?

Type values in the input box, separated by spaces or new lines. std::cin reads them in order.

Is my code uploaded to a server?

No. Your code is compiled and run entirely in your browser. Only the compiler is downloaded from a public CDN (jsDelivr) on first use.

Format references

Tool page updated: 2026-10-22