.NET/Java PDF, Tiff, Barcode SDK Library

We saw break already in a switch statement in Example 2-11 we used it to say that we re done with the switch and want to break out of that statement. The break keyword does the same thing in a loop:

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Table 12.1 Ajax options for the AjaxOptions class Description Specifies the HTTP method, which can be GET or POST. The default is GET. Specifies the element that will receive the content. Sets the insertion mode, which can be InsertBefore, InsertAfter, or Replace. Specifies the JavaScript function to be called before invoking the action. Specifies the JavaScript function to be called after the response comes back. Specifies the JavaScript function to be called in the event of an error. Specifies the JavaScript function to be called if no errors occur. Sets the confirmation message to be displayed in an OK/Cancel dialog box before proceeding. Specifies the URL to use if the anchor tag has a different destination than the Ajax request. Specifies an element that displays Ajax progress. The element should be marked as visibility:hidden initially.

using (StreamReader times = File.OpenText("LapTimes.txt")) { while (!times.EndOfStream) { string line = times.ReadLine(); if (line == "STOP!") { break; } double lapEndTime = double.Parse(line); Console.WriteLine(lapEndTime); } }

This is the loop from Example 2-16, modified to stop if it comes across a line in the input file that contains the text STOP! This breaks out immediately, abandoning the rest of the loop and leaping straight to the first line of code after the enclosing loop s closing brace. (In that case, this happens to be the enclosing using statement s closing brace, which will close the file handle.)

I started the chapter covering development processes and how I tend to develop a site in two phases: development and theming. During the development phase, I configure modules, set up blocks, add content, and upload images before I even begin to think about adding HTML or CSS. I talked about how I develop incrementally, installing Drupal and then building one section (that is, content type + blocks) at a time. I then talked about several important Drupal topics, including blocks, menus, and themes. You learned that blocks are displayed in regions and can be easily arranged through the block configuration form. You also learned that blocks display content from a number of sources, such as menus, modules, and userentered content. They also have a number of settings to determine which page and to whom the block is displayed. I closed the chapter discussing themes and how you can easily switch a theme and configure a theme to display various page elements.

Representing UI concepts in code Defining the presentation model Representing user input Scaling to complex scenarios

Some people regard this use of break as bad practice. It makes it harder to understand the loop. When a loop contains no break statements, you can understand its lifetime by looking at the while (or for, or foreach) part. But if there are break statements, you need to look at more of the code to get a complete understanding of when the loop will finish. More generally, flow control that jumps suddenly out of the middle of a construct is frowned upon, because it makes it much harder for someone to understand how execution flows through a program, and programs that are hard to understand tend to be buggy. The computer scientist Edsger Dijkstra submitted a short letter on this topic in 1968 to an academic journal, which was printed under a now infamous heading, Go-to statement considered harmful . If you re interested in iconic pieces of computing history, or if you d like a detailed explanation of exactly why this sort of jumpy flow control is problematic, you can find the original letter at http://www.cs.utexas.edu/users/EWD/ewd02xx/ EWD215.PDF.

To recap what we ve explored so far, we ve seen how to work with variables to hold information, how to write expressions that perform calculations, how to use selection statements that decide what to do, and how to build iteration statements that can do things repeatedly. There s one more basic C# programming feature we need to look at to cover the most important everyday coding features: methods.