Your Development Environment
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, plain-text 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 WordPerfect, 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.
NOTE:Most C++ compilers don't care what extension you give your source code, but if you don't specify otherwise, many will use .CPP by default. DO use a simple text editor to create your source code, or use the built-in editor that comes with your compiler. DON'T use a word processor that saves special formatting characters. If you do use a word processor, save the file as ASCII text. DO save your files with the .C, .CP, or .CPP extension. DO check your documentation for specifics about your compiler and linker to ensure that you know how to compile and link your programs.
Compiling the Source Code
Although the source code in your file is somewhat cryptic, and anyone who doesn't know C++ will struggle to understand what it is for, it is still in what we call human-readable form. Your source code file is not a program, and it can't be executed, or run, as a program can.
To turn your source code into a program, you use a compiler. How you invoke your compiler, and how you tell it where to find your source code, will vary from compiler to compiler; check your documentation. In Borland's Turbo C++ you pick the RUN menu command or type
tc <filename> from the command line, where <filename> is the name of your source code file (for example, test.cpp). Other compilers may do things slightly differently.
NOTE:If you compile the source code from the operating system's command line, you should type the following:
For the Borland C++ compiler: bcc <filename>
For the Borland C++ for Windows compiler: bcc <filename>
For the Borland Turbo C++ compiler: tc <filename>
For the Microsoft compilers: cl <filename>
After your source code is compiled, an object file is produced. This file is often named with the extension .OBJ. This is still not an executable program, however. To turn this into an executable program, you must run your linker.
Creating an Executable File with the Linker
C++ programs are typically created by linking together one or more OBJ files with one or more libraries. A library is a collection of linkable files that were supplied with your compiler, that you purchased separately, or that you created and compiled. All C++ compilers come with a library of useful functions (or procedures) and classes that you can include in your program. A function is a block of code that performs a service, such as adding two numbers or printing to the screen. A class is a collection of data and related functions; we'll be talking about classes a lot, starting on Day 5, "Functions."
The steps to create an executable file are
1. Create a source code file, with a .CPP extension.
2. Compile the source code into a file with the .OBJ extension.
3. Link your OBJ file with any needed libraries to produce an executable program.
The Development Cycle
If every program worked the first time you tried it, that would be the complete development cycle: Write the program, compile the source code, link the program, and run it. Unfortunately, almost every program, no matter how trivial, can and will have errors, or bugs, in the program. Some bugs will cause the compile to fail, some will cause the link to fail, and some will only show up when you run the program.
Whatever type of bug you find, you must fix it, and that involves editing your source code, recompiling and relinking, and then rerunning the program. This cycle is represented in Figure 1.1, which diagrams the steps in the development cycle.
Figure 1.1. The steps in the development of a C++ program.
HELLO.CPPYour First C++ Program
Traditional programming books begin by writing the words Hello World to the screen, or a variation on that statement. This time-honored tradition is carried on here.
Type the first program directly into your editor, exactly as shown. Once you are certain it is correct, save the file, compile it, link it, and run it. It will print the words Hello World to your screen. Don't worry too much about how it works, this is really just to get you comfortable with the development cycle. Every aspect of this program will be covered over the next couple of days.
WARNING: The following listing contains line numbers on the left. These numbers are for reference within the book. They should not be typed in to your editor. For example, in line 1 of Listing 1.1, you should enter: #include <iostream.h>
Listing 1.1. HELLO.CPP, the Hello World program.
1: #include <iostream.h> 2: 3: int main() 4: { 5: cout << "Hello World!\n"; 6: return 0; 7: } Make certain you enter this exactly as shown. Pay careful attention to the punctuation. The << in line 5 is the redirection symbol, produced on most keyboards by holding the Shift key and pressing the comma key twice. Line 5 ends with a semicolon; don't leave this off!
Also check to make sure you are following your compiler directions properly. Most compilers will link automatically, but check your documentation. If you get errors, look over your code carefully and determine how it is different from the above. If you see an error on line 1, such as cannot find file iostream.h, check your compiler documentation for directions on setting up your include path or environment variables. If you receive an error that there is no prototype for main, add the line int main(); just before line 3. You will need to add this line before the beginning of the main function in every program in this book. Most compilers don't require this, but a few do.
Your finished program will look like this:
1: #include <iostream.h> 2: 3: 4: int main(); 5: { 6: cout <<"Hello World!\n"; 7: return 0; 8: } Try running HELLO.EXE; it should write
Hello World! directly to your screen. If so, congratulations! You've just entered, compiled, and run your first C++ program. It may not look like much, but almost every professional C++ programmer started out with this exact program.
Compile Errors
Compile-time errors can occur for any number of reasons. Usually they are a result of a typo or other inadvertent minor error. Good compilers will not only tell you what you did wrong, they'll point you to the exact place in your code where you made the mistake. The great ones will even suggest a remedy!
You can see this by intentionally putting an error into your program. If HELLO.CPP ran smoothly, edit it now and remove the closing brace on line 6. Your program will now look like Listing 1.2.
Listing 1.2. Demonstration of compiler error.
1: #include <iostream.h> 2: 3: int main() 4: { 5: cout << "Hello World!\n"; 6: return 0;
Recompile your program and you should see an error that looks similar to the following:
Hello.cpp, line 5: Compound statement missing terminating } in function main(). This error tells you the file and line number of the problem, and what the problem is (although I admit it is somewhat cryptic). Note that the error message points you to line 5. The compiler wasn't sure if you intended to put the closing brace before or after the cout statement on line 5. Sometimes the errors just get you to the general vicinity of the problem. If a compiler could perfectly identify every problem, it would fix the code itself.
Summary
After reading this chapter, you should have a good understanding of how C++ evolved and what problems it was designed to solve. You should feel confident that learning C++ is the right choice for anyone interested in programming in the next decade. C++ provides the tools of object-oriented programming and the performance of a systems-level language, which makes C++ the development language of choice.
Today you learned how to enter, compile, link, and run your first C++ program, and what the normal development cycle is. You also learned a little of what object-oriented programming is all about. You will return to these topics during the next three weeks.
Q&A
Q. What is the difference between a text editor and a word processor?
A. A text editor produces files with plain text in them. There are no formatting commands or other special symbols required by a particular word processor. Text files do not have automatic word wrap, bold print, italics, and so forth.
Q. If my compiler has a built-in editor, must I use it?
A. Almost all compilers will compile code produced by any text editor. The advantages of using the built-in text editor, however, might include the ability to quickly move back and forth between the edit and compile steps of the development cycle. Sophisticated compilers include a fully integrated development environment, allowing the programmer to access help files, edit, and compile the code in place, and to resolve compile and link errors without ever leaving the environment.
Q. Can I ignore warning messages from my compiler?
A. Many books hedge on this one, but I'll stake myself to this position: No! Get into the habit, from day one, of treating warning messages as errors. C++ uses the compiler to warn you when you are doing something you may not intend. Heed those warnings, and do what is required to make them go away.
Q. What is compile time?
A. Compile time is the time when you run your compiler, as opposed to link time (when you run the linker) or run-time (when running the program). This is just programmer shorthand to identify the three times when errors usually surface.
Workshop
The Workshop provides quiz questions to help you solidify your understanding of the material covered and exercises to provide you with experience in using what you've learned. Try to answer the quiz and exercise questions before checking the answers in Appendix D, and make sure you understand the answers before continuing to the next chapter.
Quiz
1. What is the difference between an interpreter and a compiler?
2. How do you compile the source code with your compiler?
3. What does the linker do?
4. What are the steps in the normal development cycle?
Exercises
1. Look at the following program and try to guess what it does without running it.
1: #include <iostream.h> 2: int main() 3: { 4: int x = 5; 5: int y = 7; 6: cout "\n"; 7: cout << x + y << " " << x * y; 8: cout "\n"; 9:return 0; 10: } 2. Type in the program from Exercise 1, and then compile and link it. What does it do? Does it do what you guessed?
3. Type in the following program and compile it. What error do you receive?
1: include <iostream.h> 2: int main() 3: { 4: cout << "Hello World\n"; 5: return 0; 6: }
