MinGW c++ compiler zlib1.dll missing error?

I had this same problem, but fixed it like this:

1. I ran the MinGW Installation Manager (e.g. C:\MinGW\libexec\mingw-get\guimain.exe).

2. I navigated to All Packages -> MinGW -> MinGW Libraries.

3. I checked the boxes next to mingw32-libz (dev & dll).

   

4. I went to Installation -> Apply Changes.

Now everything worked properly.