Why my C++ codes (#includes not resolved) changed after rebuilding my program in another day? [closed]

  c++, eclipse, include, libraries

I am a beginner in C++. I wrote a program which I included iostream, and another library like portAudioAPI. yesterday my problem was that only portAudioApI could not be resolved in my program. today even all my standard libraries are gone, and even iostram can not be resolved.
I have no idea what happend to my codes, I tried to switch my workspace, but haven’t solved my problem.
I am wondering if I deleted some files , somewhere, or what happend?

Source: Windows Questions C++