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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_460</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_459.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_460</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_461.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 460</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">In the preceding chapters, we introduced C++ statements for sequence, selection, loop, and subprogram. In some cases, we introduced more than one way of implementing these structures. For example, selection may be implemented by an If-Then statement or an If-Then-Else statement. The If-Then is sufficient to implement any selection structure, but C++ provides the If-Then-Else for convenience because the two-way branch is frequently used in programming.</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">This chapter introduces five new statements that are also nonessential to, but nonetheless convenient for, programming. One, the Switch statement, makes it easier to write selection structures that have many branches. Two new looping statements, For and Do-While, make it easier to program certain types of loops. The other two statements, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">break</font><font face="Times New Roman, Times, Serif" size="3"> and </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">continue</font><font face="Times New Roman, Times, Serif" size="3">, are control statements that are used as part of larger looping and selection structures.</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="17"></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 Switch Statement</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 Switch statement is a selection control structure that allows us to list any number of branches. In other words, it is a control structure for multiway branches. A Switch is similar to nested If statements. The value of the switch expressionan expression whose value is matched with a label attached to a branchdetermines which one of the branches is executed. For example, look at the following statement:</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">switch聽(letter)<br />{<br />聽聽聽聽case聽X聽:聽Statement1;<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽break;<br />聽聽聽聽case聽L聽:<br />聽聽聽聽case聽M聽:聽Statement2;<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽break;<br />聽聽聽聽case聽S聽:聽Statement3;<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽break;<br />聽聽聽聽default聽聽:聽Statement4;<br />}<br />Statement5;</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">In this example, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">letter</font><font face="Times New Roman, Times, Serif" size="3"> is the switch expression. The statement means If </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">letter</font><font face="Times New Roman, Times, Serif" size="3"> is X, execute Statement1 and break out of the Switch statement, continuing with Statement5. If </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">letter</font><font face="Times New Roman, Times, Serif" size="3"> is L or M, execute Statement2 and continue with Statement5. If </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">letter</font><font face="Times New Roman, Times, Serif" size="3"> is S, execute Statement3 and continue with Statement5. If </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">letter</font><font face="Times New Roman, Times, Serif" size="3"> is none of the characters mentioned, execute</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_459.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_460</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_461.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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