LISTING 3.9 continued

15:Console.WriteLine(“\nmy_variable is {0}”, my_variable );

16:Console.WriteLine(“\nPI is {0}”, PI );

17:}

18:}

ANALYSIS Lines 12 and 13 declare an int and a double. Lines 15 and 16 print these values. This listing operates like those you’ve seen earlier, except it uses the .NET data

types.

In your C# programs, you should use the simple data types rather than the .NET types. All the functionality that the .NET types have is available to you in the simpler commands that C# provides. You should, however, understand that the simple C# data types translate to .NET equivalents. You’ll find that all other programming languages that work with the Microsoft .NET types also have data types that translate to these .NET types.

Literals Versus Variables

In the examples you’ve looked at so far, you have seen a lot of numbers and values used that were not variables. Often, you will want to type a number or value

into your source code. A literal value stands on its own within the source code. For example, in the following lines of code, the number 10 and the value “Bob is a fish” are literal values. As you can see, literal values can be put into variables.

int x = 10;

myStringValue = “Bob is a fish”;

Numeric Literals

In many of the examples, you have used numeric literals. By default, a numeric literal is either an int or a double. It is an int if it is a whole number, and it is a double if it is a floating-point number. For example, consider the following:

nbr = 100;

In this example, 100 is a numeric literal. By default, it is considered to be of type int, regardless of what data type the nbr variable is. Now consider the following:

nbr = 99.9;

In this example, 99.9 is also a numeric literal; however, it is of type double by default. Again, this is regardless of the data type that nbr is. This is true even though 99.9 could be stored in a type float. In the following line of code, is 100. an int or a double?

x = 100.;

When you use an integer value, it is put into an int, uint, long, or ulong depending on its size. If it will fit in an int or uint, it will be. If not, it will be put into a long or ulong. If you want to specify the data type of the literal, you can use a suffix on the literal. For example, to use the number 10 as a literal long value(signed or unsigned), you write it like the following:

10L;

You can make an unsigned value by using a u or a U. If you want an unsigned literal long value, you can combine the two suffixes: ul.

Floating-Point Literal Defaults

As stated earlier, by default, a decimal value literal is a double. To declare a literal that is of type float, you include an f or F after the number. For example, to assign the number 4.4 to a float variable, my_float, you use the following:

my_float = 4.4f;

To declare a literal of type decimal, you use a suffix of m or M. For example, the following line declares my_decimal to be equal to the decimal number 1.32.

my_decimal = 1.32m;

Boolean Literals (true and false)

Boolean literals have already been covered. The values true and false are literal. They also happen to be keywords.

String Literals

When you put characters together, they make words, phrases, and sentences. In programming parlance, a group of characters is called a string. A string can be identified because it is contained between a set of double quotes. You have actually been using strings in the examples so far. For example, the Console.WriteLine routine uses a string. A string literal is any set of characters between double quotes. The following are examples of strings:

“Hello, World!”

“My Name is Bradley”

“1234567890”

Because these numbers are between quotation marks, the last example is treated as a string literal rather than as a numeric literal.

Constants

In addition to using literals, there are times when you want to put a value in a variable and freeze it. For example, if you declare a variable called PI and you set it to 3.1459, you want it to stay 3.1459. There is no reason to change it. Additionally, you want to prevent people from changing it.

To declare a variable to hold a constant value, you use the const keyword. For example, to declare PI as stated, you use the following:

const float PI = 3.1459;

You can use PI in a program; however, you will never be able to change its value. The const keyword freezes its contents. You can use the const keyword on any variable of any data type.

Reference Types

To this point, you have seen a number of different data types. C# offers two primary ways of storing information: by value (byval) and by reference (byref). The basic data types that you have learned about store information by value.

Storing information by reference is a little more complicated. If a variable stores by reference, rather than storing the information in itself, it stores the location of the information. In other words, it stores a reference to the information. For example, if x is a “by reference” variable, it contains information on where the value 123 is located. It does not store the value 123. Figure 3.1 illustrates the difference.

The data types used by C# that store by reference are

•Classes

•Strings

•Interfaces

•Arrays

•Delegates

Each of these data types is covered in detail throughout the rest of this book.