C++ Primer Plus

Be aware of the fact that a particular compiler accepts a program doesn’t necessarily mean that the program is valid C++. And the fact that a particular compiler rejects a program doesn’t necessarily mean that the program is invalid C++. However, current compilers are more compliant with the Standard than their predecessors of a few years ago. Also compilers typically have options to control how strict the compiler is.

Tip

Occasionally, compilers get confused after incompletely building a program and respond by giving meaningless error messages that cannot be fixed. In such cases, you can clear things up by selecting Build All to restart the process from scratch. Unfortunately, it is difficult to distinguish this situation from the more common one in which the error messages merely seem to be meaningless.

Usually, the IDE lets you run the program in an auxiliary window. Some IDEs close the window as soon as the program finishes execution, and some leave it open. If your compiler closes the window, you’ll have a hard time seeing the output unless you have quick eyes and a photographic memory. To see the output, you must place some additional code at the end of the program:

      cin.get();  // add this statement

      cin.get();  // and maybe this, too

      return 0;

}

The cin.get() statement reads the next keystroke, so this statement causes the program to wait until you press the Enter key. (No keystrokes get sent to a program until you press Enter, so there’s no point in pressing another key.) The second statement is needed if the program otherwise leaves an unprocessed keystroke after its regular input. For example, if you enter a number, you type the number and then press Enter. The program reads the number but leaves the Enter keystroke unprocessed, and it is then read by the first cin.get().

C++ on the Macintosh

Apple currently supplies a developer framework called Xcode with the Mac OS X operating system. It’s free but normally not preinstalled. You can install it from the operating system installation disks, or you can download it for a nominal fee from Apple. (Be aware that it is over a 4GB download.) Not only does it provide an IDE that supports several programming languages, it also installs a couple of compilers—g++ and clang—that can be used as command-line programs in the Unix mode accessible through the Terminal utility.

Tip

For IDEs: To save time, you can use just one project for all the sample programs. Just delete the previous sample source code file from the project list and add the current source code. This saves time, effort, and lessens disk clutter.

Summary

As computers have grown more powerful, computer programs have become larger and more complex. In response to these conditions, computer languages have evolved so that it’s easier to manage the programming process. The C language incorporated features such as control structures and functions to better control the flow of a program and to enable a more structured, modular approach. To these tools C++ adds support for object-oriented programming and generic programming. This enables even more modularity and facilitates the creation of reusable code, which saves time and increases program reliability.

The popularity of C++ has resulted in a large number of implementations for many computing platforms; the C++ ISO standards (C++98/03 and C++11) provide a basis for keeping these many implementations mutually compatible. The standards establishes the features the language should have, the behavior the language should display, and a standard library of functions, classes, and templates. The standards supports the goal of a portable language across different computing platforms and different implementations of the language.

To create a C++ program, you create one or more source files containing the program as expressed in the C++ language. These are text files that must be compiled and linked to produce the machine-language files that constitute executable programs. These tasks are often accomplished in an IDE that provides a text editor for creating the source files, a compiler and a linker for producing executable files, and other resources, such as project management and debugging capabilities. But the same tasks can also be performed in a command-line environment by invoking the appropriate tools individually.

2. Setting Out to C++

In this chapter you’ll learn about the following:

• Creating a C++ program

• The general format for a C++ program

• The #include directive

• The main() function

• Using the cout object for output

• Placing comments in a C++ program

• How and when to use endl

• Declaring and using variables

• Using the cin object for input

• Defining and using simple functions