Are there any scripts for compiling C code with cygwin for nppexec?
Read the Modern C book.
Avoid weird characters (notably spaces) in C source file names. So use foo-bar.c or foo_bar.c but not foo bar.c (with a space after second o).
For your source code editor, consider GNU emacs or vim or Visual Studio Code (or some other IDE of your choice). But remember that most C compiler programs (including tinycc, nwcc, GCC -which cygwin provides-, Clang, even Visual Studio is at heart its cl command) are transforming a C translation unit (practically your foo.c file) into an object file (e.g. foo.obj on Windows, foo.o on Linux or MacOSX) and don't have natively any GUI for that. Later some linker is needed.
Compile thru a build automation tool such as ninja or GNU make.
Use a version control system, such as git.
In many cases, it is interesting to generate some of your C code (so called meta-programming approaches). Look into tools like SWIG, ANTLR, GNU bison, rpcgen, or those supporting ASN-1 listed here. For GUI interfaces, consider using GTK and related code generator tools, such as Ggen. For JSONRPC services, see jsvggen. With a command line interface approach, taking advantage of these tools is easy. Look also, for inspiration, into the open source code of many bootstrapped source to source compilers emitting C code, such as Bigloo or Chicken/Scheme or S48.
Learn to use a debugger, such as GDB or LLDB. Debugging information (e.g. DWARF) needs special flags at compilation time, so with GCC, use gcc -Wall -Wextra -g to get warnings and debug info.
Cygwin is wrapping the GCC compiler.
For embedded cross-compilation for Arduino or RaspBerryPI devices, the C cross-compiler is also a command-line tool.
Spend several days to read the documentation of cygwin and of GCC.
Of course, read the documentation of every tool mentioned here.
Cygwin is Unix inspired, so be aware of the Unix philosophy.
NppExec is a plugin for Notepad++ which has its documentation somewhere.
For inspiration, study the source code of existing open source software on github and gitlab.
PS. Consider perhaps installing a newbie-friendly Linux distribution such as Debian or Ubuntu on your PC laptop (if you prefer the original: a good GNU/Linux distribution to its imitation: Cygwin). Be sure to backup your important data before trying. You'll need a hundred gigabytes of disk space to be at ease, and you could have a dual boot setting: Linux for software development, Windows for games.
PPS: every software mentioned above (except some MicroSoft compilers) is open source and exists on Debian or on Ubuntu. You could later be interested by Linux From Scratch. Read also for your information this draft report (work in progress in June 2020).