error LNK2001: unresolved external symbol _main
In your project properties (that's what appears when you press Alt+F7) there's a tree on the left.
Under "Configuration Properties" there's an entry "Linker", under "Linker" there's an entry "System" - select it.
On the right a couple of options appear.
In the option "SubSystem" you can select either "Console" or "Windows".
"Console" assumes a function called "main" which should be defines as
int main(int argc, char *argv[])
{
}"Windows" assumes a function called "WinMain" defined as
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
}if you use "Console" (and the associated main(...) function), a console windows opens automatically when your application starts. That's because C++ originates from unix development and expects some sort of textual output device.
This is quite useful as long as you're in development to print all sorts of debug-infos.
For "Windows" applications (with the associated WinMain(...) function) this is usually undesired as there's some sort of gui.
Please recapitulate what I wrote earlier about storing project- and source-files in a single place to avoid mess-up.