Learning C# 3.0

WriteLine( ) and Output

The .NET Framework provides a useful method for displaying output on the screen in console applications: System.Console.WriteLine( ). How you use this method will become clearer as you progress through the book, but the fundamentals are straightforward. You call the method, and in the parentheses you pass in a string that you want printed to the console (the screen), as in the Hello World application in Chapter 1.

That’s useful; a string is fixed text, and you might want to output a value that can change, depending on the content of your program. For that, you can also pass in substitution parameters. A substitution parameter is just a placeholder for a value you want to display. For example, you might pass in the substitution parameter {0} as part of the string, and then when you run the program, you’ll substitute the value held in the variable myInt so that its value is displayed where the parameter {0} appears in the WriteLine( ) statement.

Here’s how it works. Each substitution parameter is a number between braces, starting with 0 for the first parameter, 1 for the next, and so on. So, if you’re using just one substitution parameter, it might look like this:

System.Console.WriteLine("Age of student: {0}", myInt);

Notice that you follow the quoted string with a comma and then a variable name. The value of the variable will be substituted into the parameter. If myInt has the value 15, the statement shown previously causes the following to display:

Age of student: ...