I have two questions?
1-Is the quality of a picture related to its number of pixels?(I know its not related to c++)
2-Is it possible to work with individual pixels of a picture via c++?

1. What's the quality of a picture? Imagine 1-pixel picture... 2-pixels picture... and so on ;)
2. There are lots of C and C++ libraries (search Google). I think now most of graphics applications are written in C and C++.
What's a picture? It's a file. What's a file? It's a sequence of bytes. What's a byte? It's a sequence of bits. What's a problem? ;)