This book makes the assumption that your computer has a mode in which you can write directly to the screen,without worrying about a graphical environment, such as the ones in Windows or on the Macintosh.
Your compiler may have its own built-in text editor, or you may be using a commercial text editor or word processor that can produce text files. The important thing is that whatever you write your program in, it must save simple, plaintext files, with no word processing commands embedded in the text. Examples of safe editors include Windows Notepad, the DOS Edit command, Brief, Epsilon, EMACS, and vi. Many commercial word processors, such as Word Perfect, Word, and dozens of others, also offer a method for saving simple text files.
The files you create with your editor are called source files, and for C++ they typically are named with the extension .CPP, .CP, or .C. In this book, we'll name all the source code files with the .CPP extension, but check your compiler for what it needs.