Example: Hello, DLL

hello.c

#include <stdio.h>

__declspec(dllexport)
void hello(void)
{
    printf("Hello, DLL\n");
}

main.c

#include <windows.h>

int main(void)
{
    HMODULE h = LoadLibraryA("hello.dll");
    void (*hello)(void) = (void (*)(void)) GetProcAddress(h, "hello");
    hello();
    FreeLibrary(h);

    return 0;
}

Makefile

all: main.exe hello.dll

main.exe: main.c
        x86_64-w64-mingw32-gcc -o main.exe main.c

hello.dll: hello.c
        x86_64-w64-mingw32-gcc -shared -o hello.dll hello.c

clean:
        rm -f main.exe hello.dll