Wednesday, August 5, 2009

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.

Listing 1.1. HELLO.CPP, the Hello World program.

1: #include
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 << style="font-weight: bold;">Your finished program will look like this:


1: #include
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
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.

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