What you need is a text editor. Most of them are free. I would suggest to take a look at Visual Studio Code. It's a free, open-sourced text editor, made by Microsoft. It provides a great arsenal of features out of the box like:
The editor runs on every major platform and is updated on a montly bases. Make yourself a favor and don't use notepad for programming. You are a plethora of tools available, every one better than notepad.
If you don't like Visual Studio Code, you can take a look at Sublime Text (paid, with unlimited trial period), Atom (another great text editor), Brackets (not that popular, but still better than Notepad).