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.NET/Java PDF, Tiff, Barcode SDK Library<script type="text/javascript"> var xmlHttp; function createXMLHttpRequest() { if (window.ActiveXObject) { xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); } else if (window.XMLHttpRequest) { xmlHttp = new XMLHttpRequest(); } } function startRequest() { createXMLHttpRequest(); xmlHttp.onreadystatechange = handleStateChange; xmlHttp.open("GET", "simpleResponse.xml", true); xmlHttp.send(null); } function handleStateChange() { if(xmlHttp.readyState == 4) { if(xmlHttp.status == 200) { alert("The server replied with: " + xmlHttp.responseText); } } } </script> </head> <body> <form action="#"> <input type="button" value="Start Basic Asynchronous Request" onclick="startRequest();"/> </form> </body> </html> The server s response file, simpleResponse.xml, contains only a single line of text. Clicking the button on the HTML page should produce an alert box with the contents of the simpleResponse.xml file. Figure 2-4 displays the identical alert boxes that contain the server s response in both Internet Explorer and Firefox. creare barcode excel 2013, free barcode software for excel 2007, excel barcode, barcode excel 2007, barcode activex in microsoft office excel 2010, how do i create barcodes in excel 2010, excel 2010 barcode add in, barcode excel 2007 freeware, how to create barcodes in excel 2013 free, how to print a barcode in excel 2010,CHAPTER 2 I HOW TO OBTAIN, INSTALL, AND USE F# Figure 13-42. LEDs and LDR for Color Sensor The Color Sensor schematic is shown in Figure 13-43. Values for R3, R4, and R5 are carefully selected to make the LEDs produce a balanced amount of light, and you might need to adjust their values for your particular LEDs. Use the brightest LEDs you can get and a pure green green LED if possible. The resistors are adjusted by calibrating the sensor to a white object and making all three colors read the same value. The results of this example, when compiled and executed, are as follows: Green frog, Is your body also freshly painted In a regular for loop, the initial value of the counter must always be less than the final value, and the value of the counter will increase as the loop continues There is a variation on this, where to is replaced by downto In this case, the initial counter value must always be greater than the final value, and the counter will decrease as the loop continues An example of how to use downto is as follows: #light let shusonKato = [| "watching"; "been "; "have "; "children "; "three "; "my "; "realize "; "and "; "ant "; "an "; "kill "; "I "; |] for index = Arraylength shusonKato - 1 downto 0 do print_string shusonKato. The request to the server was sent asynchronously, allowing the browser to continue responding to user input while awaiting the server s response in the background. If a synchronous operation was chosen and if the server s response had taken several seconds to arrive, the browser would have been unresponsive to user input during the waiting time. The asynchronous behavior, while subtle, can measurably improve the end user s experience by avoiding the appearance that the browser has frozen and is failing to respond to user input. This allows the user to continue working while the server works on the previous request in the background. The ability to communicate with the server without interrupting the user s workflow opens a wide variety of techniques for improving the user experience. One application, for example, is for validating user input. While a user is filling out the fields on an input form, the browser could periodically send the form values to the server for validation, without interrupting the user filling in the remaining form fields. If a validation rule fails, the user could be notified immediately, before the form is actually sent to the server for processing, saving the user time and reducing the load on the server, as the form s contents don t have to be rebuilt after an unsuccessful form submission. [index] The results of this example, when compiled and executed, are as follows: I kill an ant and realize my three children have been watching The while loop is another familiar imperative language construct It is an expression that creates a loop over a section of code until a Boolean expression changes to false To create a while loop in F#, you use the keyword while followed by a Boolean expression that determines whether the loop should continue As with for loops, you place the body of the loop between the keywords do and done, and the body should have type unit; otherwise, the compiler will issue a warning Here s an example of a while loop: #light let matsuoBasho = ref [ "An "; "old "; "pond! "; "A "; "frog "; "jumps "; "in- "; "The "; "sound "; "of "; "water" ] while (List. Figure 13-43. Color Sensor schematic Table 13-8 has the complete bill of materials. Table 13-8. Color Sensor Bill of Materials
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