Online C++ Compiler - online editor
https://www.onlinegdb.com/online_c++_compiler
OnlineGDB is online IDE with C++ compiler. Quick and easy way to compiler c++ program online. It supports g++ compiler for c++.
Online Compiler and IDE >> C/C++, Java, PHP, Python... - Ideone.com
https://ideone.com/
Ideone is an online compiler and debugging tool which allows you to compile source code and execute it online in more than 60 programming languages.
Repl.it - Online C++ Editor and IDE - Fast, Powerful, Free
https://repl.it/languages/cpp
Online C++ compiler, Online C++ IDE, and online C++ REPL.