C / C++ Playground (WASM)

Compile and run C/C++ code in the browser via Emscripten WASM with console output and errors.

Tested tool guide Tested browser tools Checked August 16, 2026

What C / C++ Playground (WASM) does, with a checked example

Paste a C or C++ program to compile it with Emscripten and run the resulting WebAssembly in the current browser. The console presents text produced by the program along with compilation or execution errors, making the playground useful for focused experiments and portable examples. Compilation and execution happen locally in the browser; source code is not uploaded. The important surprise is that this is a browser-targeted WebAssembly environment, not a native desktop process, so operating-system APIs and platform-specific libraries may behave differently or be unavailable.

Worked example

A concrete input and expected output from the current implementation.

Input

#include <stdio.h>

int main(void) {
    int width = 7;
    int height = 5;
    printf("%d\n", width * height);
    return 0;
}

Expected output

The program multiplies 7 by 5 and passes the resulting integer, 35, to printf. The newline character ends the console line.

How the result is produced

Compilation and execution

Enter a complete C or C++ source file, normally including a main function. Emscripten compiles the source for WebAssembly. If compilation succeeds, the generated program runs in the browser and text written to standard output or standard error appears in the console. A compilation failure prevents the program from running and produces compiler diagnostics instead.

Reading the console

The console shows what the compiled program writes; it does not automatically display every expression or variable. Use functions such as printf in C or output streams such as std::cout in C++ when a value must be visible. Compiler diagnostics concern source translation, while messages produced after a successful build belong to the running WebAssembly program.

Good uses

Check whether a short C or C++ example compiles under Emscripten.
Test arithmetic, control flow, string handling, or standard console output without installing a compiler.
Reproduce a small compiler diagnostic or browser-side WebAssembly behavior before adding code to a larger project.

Limits and checks

A successful run demonstrates behavior for this Emscripten WebAssembly target, not necessarily for every native compiler or operating system.
Undefined behavior can appear to produce a stable answer; one observed result does not make such code valid or portable.
Headers, libraries, system calls, compiler options, and hardware-specific features available in a desktop toolchain may not be available here.

Common questions

Can it run an existing desktop C or C++ application unchanged?

Sometimes, but not reliably. Self-contained code using supported language and library features is the best fit. Applications tied to native windows, device access, operating-system services, dynamically loaded native libraries, or a particular desktop build system usually require porting. The playground runs WebAssembly in a browser rather than producing or launching a native executable.

Why is the console empty even though compilation succeeded?

Successful compilation does not imply visible output. Calculating a value, assigning a variable, or returning zero from main does not print that value. Add an explicit printf, puts, std::cout, or std::cerr operation. An empty console can also result when the executed path never reaches the output statement, so inspect conditions and early returns.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.