Every string is supposed to end with a null byte ('\0'). in concat, are you terminating phrase1 with a null byte when you copy phrase2 to the end of phrase1? In copy, are you stopping at the end of...

To echo vmanes, I recommend wxWidgets. It is simpler and easier to use than the WinAPI, and it is portable to other platforms. QT is nice, but there are license fees for use on Window. Also, take...

Every ISO standard C/C++ program must have a main(). Windows, other graphic environments, and many embedded systems have a non-standard environment and may not need a main().

So, the answer is:...