3. Dealing with Data

In this chapter you’ll learn about the following:

• Rules for naming C++ variables

• C++’s built-in integer types: unsigned long, long, unsigned int, int, unsigned short, short, char, unsigned char, signed char, bool

• C++11’s additions: unsigned long long and long long

• The climits file, which represents system limits for various integer types

• Numeric literals (constants) of various integer types

• Using the const qualifier to create symbolic constants

• C++’s built-in floating-point types: float, double, and long double

• The cfloat file, which represents system limits for various floating-point types

• Numeric literals of various floating-point types

• C++’s arithmetic operators

• Automatic type conversions

• Forced type conversions (type casts)

The essence of object-oriented programming (OOP) is designing and extending your own data types. Designing your own data types represents an effort to make a type match the data. If you do this properly, you’ll find it much simpler to work with the data later. But before you can create your own types, you must know and understand the types that are built in to C++ because those types will be your building blocks.

The built-in C++ types come in two groups: fundamental types and compound types. In this chapter you’ll meet the fundamental types, which represent integers and floating-point numbers. That might sound like just two types; however, C++ recognizes that no one integer type and no one floating-point type match all programming requirements, so it offers several variants on these two data themes. Chapter 4, “Compound Types,” follows up by covering several types that are built on the basic types; these additional compound types include arrays, strings, pointers, and structures.

Of course, a program also needs a means to identify stored data. In this chapter you’ll examine one method for doing so—using variables. Then you’ll look at how to do arithmetic in C++. Finally, you’ll see how C++ converts values from one type to another.

Simple Variables

Programs typically need to store information—perhaps the current price of Google stock, the average humidity in New York City in August, the most common letter in the U.S. Constitution and its relative frequency, or the number of available Elvis impersonators. To store an item of information in a computer, the program must keep track of three fundamental properties:

• Where the information is stored

• What value is kept there

• What kind of information is stored

The strategy the examples in this book have used so far is to declare a variable. The type used in the declaration describes the kind of information, and the variable name represents the value symbolically. For example, suppose Chief Lab Assistant Igor uses the following statements:

int braincount;
braincount = 5;

These statements tell the program that it is storing an integer and that the name braincount represents the integer’s value, 5 in this case. In essence, the program locates a chunk of memory large enough to hold an integer, notes the location, and copies the value 5 into the location. You then can use braincount later in your program to access that memory location. These statements don’t tell you (or Igor) where in memory the value is stored, but the program does keep track of that information, too. Indeed, you can use the & operator to retrieve braincount’s address in memory. You’ll learn about that operator in the next chapter, when you investigate a second strategy for identifying data—using pointers.