About the C++ runner
Use the left-hand editor to run a small C++ idea without setting up a project first. Runs C++ through Piston from main.cpp, with the wildcard version tracking the current runner image. Run it. Read the output. Then change one thing, because the fastest debugging session is usually the one with the fewest moving parts.
We built this page for short checks: STL snippets, templates in miniature, interview-style input parsing, and comparing value/reference behavior. It is deliberately narrower than a local environment, and that is the point; when a snippet is only twenty lines long, a full toolchain can get in the way of the question you actually have.
C++ lets undefined behavior hide behind perfectly normal-looking output, especially around references, iterator invalidation, and object lifetime. Use this to check a language rule or a small STL idea. Do not use it to decide whether your production build flags are correct.
Before you press Run
- Start with the smallest C++ snippet that can show the behavior.
- Add input only when the program reads it. Empty STDIN is a valid test case.
- Press Run, inspect stdout and stderr, then change one line. That rhythm keeps accidental fixes from hiding the real bug.
The mechanics are simple. We keep the run cycle compact because this page is meant to answer one question at a time, not manage a full project tree.
That style also makes the result easier to share. A reader can scan a short C++ snippet, run it, and see the same error without first recreating your directory structure or guessing which dependency you forgot to mention.
One useful experiment
The saved example below is intentionally left unchanged. Run it once as written, then make a small edit and run it again; that gives you a known-good baseline before you test your own idea.
#include <iostream>
#include <string>
#include <vector>
int main() {
std::string name;
std::cin >> name;
std::cout << "Hello, " << name << "!" << std::endl;
std::vector<int> nums = {10, 20, 30};
for (int n : nums) {
std::cout << n << " ";
}
std::cout << std::endl;
return 0;
}The next preserved block belongs to the same example. Keep it nearby when you are comparing input, output, or the shape of the result. Small examples expose mistakes quickly.
Hello, Alice!
10 20 30After the sample works, try one edge case that exercises the page's limits. C++ lets undefined behavior hide behind perfectly normal-looking output, especially around references, iterator invalidation, and object lifetime. That single change often teaches more than pasting a large program and trying to guess which part failed.
Limits first
This page is strongest when the problem is small and visible. It is weakest when the problem depends on multi-file builds, custom libraries, CMake, and ABI questions. Two caveats.
- Do not paste secrets, tokens, private URLs, or customer data.
- The environment is intentionally constrained, so a snippet that works here still deserves a local check when compiler flags, packages, server state, or exact versions matter.
- Timeouts are normal for runaway loops. They protect the shared runner.
We deliberately keep the sandbox narrow. That makes the output easier to trust for STL snippets, templates in miniature, interview-style input parsing, and comparing value/reference behavior, while making it clear when you have outgrown the page.
One practical test: if you cannot explain the snippet in one sentence, split it. The runner is happiest when each run answers a single question, and you will be happier too when the error message points at one idea instead of a pile of guesses.
FAQ notes
These answers focus on the runner's boundaries and the language details most likely to trip up a small C++ example.
What is the big 3 in C++?
The Big Three in C++ are the destructor, copy constructor, and copy assignment operator. If a class owns a resource, such as heap memory or a file handle, you usually need to think about all three. Modern C++ often tries to avoid this by using standard containers and smart pointers instead. For example, g++ main.cpp -o main is the usual local compile-and-link command.
What are the big 5 in C++?
The Big Five add the move constructor and move assignment operator to the old Big Three. They matter when a class owns a resource and should transfer it cheaply instead of copying it. If your class uses std::vector, std::string, or std::unique_ptr correctly, you may not need to write any of them. C++ accepts many C-like habits, but object lifetime, references, and overload rules can change what the same-looking code means.
Should I write a compiler in C or C++?
You can write a compiler in either C or C++. C keeps the runtime model simple and is common in low-level tools. C++ gives you stronger abstractions for syntax trees, visitors, and ownership. The better choice depends on the team and project. For learning, choose the language you can debug comfortably. For example, g++ main.cpp -o main is the usual local compile-and-link command.
Can I write C code in a C++ compiler?
Some C code compiles as C++, but not all of it. C++ is stricter about implicit conversions, has different rules for keywords, and handles function declarations differently. If you want C behavior, use a C compiler. If you are migrating to C++, start with small files and fix one category of error at a time. C++ accepts many C-like habits, but object lifetime, references, and overload rules can change what the same-looking code means.
What is GCC and gnu?
GCC is the GNU Compiler Collection. It includes compilers for C, C++, and other languages. For C you usually call gcc; for C++ you usually call g++, because it links the C++ standard library automatically. GNU is the larger free software project that maintains GCC and many related tools. For example, g++ main.cpp -o main is the usual local compile-and-link command.
how to run cpp file in terminal
Compile first with g++ filename.cpp -o programname, then run the binary with ./programname (or programname.exe on Windows). If the compile reports errors, fix them and re-run the g++ command. To skip the toolchain install, paste the same C++ code into the editor on this page and press Run.
how to compile a cpp file
Use g++ for GCC or cl for MSVC. A common command is g++ -std=c++17 myfile.cpp -o myprogram, which builds a runnable binary. Add -Wall to surface warnings, -O2 for an optimized build, and -g if you need debug symbols. On this page, the compile step runs for you when you click Run.
how to run cpp program
After compiling, run the produced executable. On Linux or macOS that's ./programname from the same folder. On Windows it's programname.exe. If your program reads input, pipe it in with ./programname < input.txt. In the browser editor here, just put input in the STDIN field and click Run.
Workflows that fit
Use it when you are stuck on someone else's machine, teaching a small concept, or separating a language question from a project question. No ceremony.
It also works well as a note-taking tool: paste the final snippet into your lesson, issue, or commit message after you have proved it in the runner.
Keep the example slightly smaller than feels natural. That sounds fussy, but it prevents a common debugging mistake: changing five pieces of code, getting a different result, and no longer knowing which piece mattered.
Where to learn more
Reference pages are better than folklore when an error message gets specific. Start with official docs, then use tutorials for context once the rule is clear.