Writing a graphical Z80 emulator in C or C++ [closed]

Answer 1

Perhaps start by looking at these:

A good tutorial can be found here: Independent Z80 Assembly Guide

Z80 DOCUMENTATION

The Undocumented Z80 Documented v0.91 (pdf)

The Complete Z80 Instruction Reference

Z80 Microprocessor Instruction Set Summary

Answer 2

I'd recommend you consider starting by writing an emulator for a slightly simpler, but related CPU, the 8080. The Z80 is actually rather complicated (multi-byte instructions, more addressing modes, index registers, etc.), whereas 8080 instructions are very easy to decode (you can just use a 256-entry lookup table, as a first-order solution).

All the code you write to control the program (display, data entry, memory dumps, etc.) should be re-useable if you then decide to go on to attempt the Z80, and indeed you should design the user interface to be simulated processor-independent.