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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_474</title> <link rel="stylesheet" href="reset.css" type="text/css" media="all"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> </head> <body> <table summary="top nav" border="0" width="100%"> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_473.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_474</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_475.html">next page ></a></td> </tr> <tr> <td align="left" colspan="3" style="background: #ffffff; padding: 20px;"> <table border="0" width="100%" cellpadding="0"><tr><td align="center"> <table border="0" cellpadding="2" cellspacing="0" width="100%"><tr><td align="left"></td> <td align="right"></td> </tr></table></td></tr><tr><td align="left"><p></p><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="right"><font face="Times New Roman, Times, Serif" size="2" color="#FF0000">Page 474</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The For loop is easier to understand and is less prone to error.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">A good rule of thumb is: Use </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">break</font><font face="Times New Roman, Times, Serif" size="3"> within loops only as a last resort. Specifically, use it only to avoid baffling combinations of multiple Boolean flags and nested Ifs.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">Another statement that alters the flow of control in a C++ program is the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">continue</font><font face="Times New Roman, Times, Serif" size="3"> statement. This statement, valid only in loops, terminates the current loop iteration (but not the entire loop). It causes an immediate branch to the bottom of the loopskipping the rest of the statements in the loop bodyin preparation for the next iteration. Here is an example of a reading loop in which we want to process only the positive numbers in an input file:</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">for聽(dataCount聽=聽1;聽dataCount聽<=聽500;聽dataCount++)<br />{<br />聽聽聽聽dataFile聽>>聽inputVal;<br />聽聽聽聽if聽(inputVal聽<=聽0)<br />聽聽聽聽聽聽聽聽continue;<br />聽聽聽聽cout聽<<聽inputVal;<br />聽聽聽聽.<br />聽聽聽聽.<br />聽聽聽聽.<br /><br />}</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">If </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">inputVal</font><font face="Times New Roman, Times, Serif" size="3"> is less than or equal to 0, control branches to the bottom of the loop. Then, as with any For loop, the computer increments </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">dataCount</font><font face="Times New Roman, Times, Serif" size="3"> and performs the loop test before going on to the next iteration.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">continue</font><font face="Times New Roman, Times, Serif" size="3"> statement is not used often, but we present it for completeness (and because you may run across it in other people's programs). Its primary purpose is to avoid obscuring the main process of the loop by indenting it within an If statement. For example, the above code would be written without a </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">continue</font><font face="Times New Roman, Times, Serif" size="3"> statement as follows:</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">for聽(dataCount聽=聽1;聽dataCount聽<=聽500;聽dataCount++)<br />{<br />聽聽聽聽dataFile聽>>聽inputVal;<br />聽聽聽聽if聽(inputVal聽>聽0)<br />聽聽聽聽{<br />聽聽聽聽聽聽聽聽cout聽<<聽inputVal;<br />聽聽聽聽聽聽聽聽.<br />聽聽聽聽聽聽聽聽.<br />聽聽聽聽聽聽聽聽.<br />聽聽聽聽}<br />}</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">Be sure to note the difference between </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">continue</font><font face="Times New Roman, Times, Serif" size="3"> and </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">break</font><font face="Times New Roman, Times, Serif" size="3">. The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">continue</font><font face="Times New Roman, Times, Serif" size="3"> statement means Abandon the current iteration of the loop, and go on to the next iteration. The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">break</font><font face="Times New Roman, Times, Serif" size="3"> statement means Exit the entire loop immediately.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><p><font size="0"></font></p>聽 </td> </tr> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_473.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_474</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_475.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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