Qt Creator
Qt Creator's advanced code editor lets you code in C++, QML, JavaScript, Python and other languages. It features code completion, syntax highlighting, refactoring and has built-in documentation at your fingertips. Qt Creator integrates with most popular version control systems, including Git, subversion, perforce, and mercurial. Integrated visual editors for building C++ widget-based applications or fluid Qt Quick-based animated UIs with ready-made controls. Import an existing project or create one from scratch – Qt Creator generates all the necessary files. Support for Cmake and cross-compiling with qmake is included. Build for and run your software on desktop, mobile and embedded operating systems. The build settings allow you to easily switch between targets. Test and debug applications in conditions practically identical to those on your target device.
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StackBlitz
Create, edit & deploy fullstack apps — in just one click. Create user interfaces that are out of this world thanks to our partnership with Progress KendoReact. Go to Definitions, and other Visual Studio Code features just work. Tweak your app in real time without page reloads while preserving your app state. Import any NPM package into your project quicker than on local. Thanks to our revolutionary in-browser dev server. Drag & Drop files and folders into the editor. No more copy + pasting, uploading, or git commands. Your app is being hosted for easy live sharing. Create new projects by simply POSTing the desired project data from a form— useful when you don't/can't use our Javascript SDK. With your desired StackBlitz project open, simply drag and drop any files and folder you want to import.
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CodePen
CodePen is a social development environment for front-end designers and developers. Build and deploy a website, show off your work, build test cases to learn and debug, and find inspiration. Find inspiration from 1.8 million+ front-end designers and developers. Browse and share work from world-class designers and developers in the front-end community. The CodePen Editor is highly customizable. There is autocomplete and Emmet for speed and accuracy. Plus you can set up smart defaults for starting new work. Completely customize the look of code demos on your own site. Change the look of your site? Just change the theme and all your Embedded Pens change too. Need to use an image in a Pen? No more awkwardly finding alternate hosting for it, you can drag-and-drop it right onto CodePen and we'll host it for you. And not just images! CSS, JSON files, SVGs, media files, whatever! Projects is the most powerful feature of CodePen.
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JSFiddle
JSFiddle has the notion of panels (or tabs if you switch into the tabbed layout), there are 4 panels, 3 where you can enter code, and 1 to see the result: HTML - structure code, no need to add body doctype head, that's added automatically, CSS - styles. You can switch pre-pocessor to SCSS, JavaScript - behavior. There are many frameworks and code pre-processors you can use. Once you enter code, just hit "Run" in the top actions bar, and the fourth panel with results will appear. SFiddle allows you to switch the layout of the editor from the classic 2x2 grid to something that suits your needs. In addition to the grids mode it also has a tabbed mode. Grids are fully resizable. As an addition resizing the Results panel will tell you its width (handy for working on media queries).
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