You create or define a variable by stating its type, followed by one or more spaces, followed by the variable name and a semicolon. The variable name can be virtually any combination of letters, but cannot contain spaces. Legal variable names include x, J23qrsnf, and myAge. Good variable names tell you what the variables are for; using good names makes it easier to understand the flow of your program. The following statement defines an integer variable called myAge:

int myAge;

As a general programming practice, avoid such horrific names as J23qrsnf, and restrict single-letter variable names (such as x or i) to variables that are used only very briefly. Try to use expressive names such as myAge or howMany. Such names are easier to understand after completing this book when you are scratching your head trying to figure out what you meant when you wrote that line of code.

Try this experiment: Guess what these pieces of programs do, based on the first few lines of code:

Example 1

main()

{

unsigned short x;

unsigned short y;

ULONG z;

z = x * y;

}

Example 2

main ()

{

unsigned short Width;

unsigned short Length;

unsigned short Area;

Area = Width * Length;

}

Clearly, the second program is easier to understand, and the inconvenience of having to type the longer variable names is more than made up for by how much easier it is to maintain the second program.

C++ is case-sensitive. In other words, uppercase and lowercase letters are considered to be different. A variable named age is different from Age, which is different from AGE.

NOTE: Some compilers allow you to turn case sensitivity off. Don’t be tempted to do this; your programs won’t work with other compilers, and other C++ programmers will be very confused by your code.

There are various conventions for how to name variables, and although it doesn’t much matter which method you adopt, it is important to be consistent throughout your program.

Many programmers prefer to use all lowercase letters for their variable names. If the name requires two words (for example, my car), there are two popular conventions: my_car or myCar. The latter form is called camel-notation, because the capitalization looks something like a camel’s hump.

Some people find the underscore character (my_car) to be easier to read, while others prefer to avoid the underscore, because it is more difficult to type. This book uses camel-notation, in which the second and all subsequent words are capitalized: myCar, theQuickBrownFox, and so forth.

Some words are reserved by C++, and you may not use them as variable names. These are keywords used by the compiler to control your program. Keywords include if, while, for, and main. Your compiler manual should provide a complete list, but generally, any reasonable name for a variable is almost certainly not a keyword.

DO define a variable by writing the type, then the variable name. DO use meaningful variable names. DO remember that C++ is case sensitive. DON’T use C++ keywords as variable names. DO understand the number of bytes each variable type consumes in memory, and what values can be stored in variables of that type. DON’T use unsigned variables for negative numbers.