HELLO.CPP Your 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.

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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>

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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.