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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_271</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_270.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_271</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_272.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 271</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"><i>(text box continued from previous page)</i></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table cellspacing="0" border="0" width="698" cellpadding="4"><tr><td valign="top"><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"><img src="80c667ad4f7d53000acfe2390cec78dc.gif" border="0" alt="0271-01.gif" width="440" height="224" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr><tr><td valign="top"><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 first part of defining a finite state machine is to provide a way in which to keep track of the current state. Because there are only two states in this problem, we can use a single Boolean <i>state variable,</i> called </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">exclamEncountered</font><font face="Times New Roman, Times, Serif" size="3">. When the variable is </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">TRUE</font><font face="Times New Roman, Times, Serif" size="3">, the machine is in one state; when the variable is </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">FALSE</font><font face="Times New Roman, Times, Serif" size="3">, it is in the other. (In our traffic light example, we would define two char variables </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">eastWest聽and聽northSouth</font><font face="Times New Roman, Times, Serif" size="3"> to be the state variables.)</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr><tr><td valign="top"><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">Next, we have to determine which state the machine is in. For this, we use an </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">If-Then-Else</font><font face="Times New Roman, Times, Serif" size="3"> structure with one branch for each possible state.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr><tr><td valign="top"><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">if聽(exclamEncountered)<br />聽聽聽聽.<br />聽聽聽聽.聽聽聽聽聽聽聽//聽Test聽for聽each聽transition聽rule聽from聽the聽state聽where<br />聽聽聽聽.<br />聽聽聽聽聽聽聽聽聽聽聽聽//聽聽聽exclamEncountered聽==聽TRUE<br />else<br />聽聽聽聽.<br />聽聽聽聽.<br />聽聽聽聽.聽聽聽聽聽聽聽//聽Test聽for聽each聽transition聽rule聽from聽the聽state聽where<br />聽聽聽聽聽聽聽聽聽聽聽聽//聽聽聽exclamEncountered聽==聽FALSE</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr><tr><td valign="top"><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">Within each state branch, we test for each transition rule that starts from that particular state. There are two rules that start from the exclamation-mark-encountered state and one that starts from the no-exclamation-mark-encountered state. Associated with each transition rule is some action that may be as simple as switching to another state, or much more complex.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr><tr><td valign="top"><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">if聽(exclamEncountered)聽聽聽聽聽聽聽聽聽聽聽//聽State聽==聽!聽encountered<br />{<br />聽聽聽if聽(currChar聽==聽=)聽聽聽聽聽聽聽聽聽聽//聽Rule:聽If聽currChar聽is聽=,<br />聽聽聽{<br />聽聽聽聽聽聽count++;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increment聽count<br />聽聽聽聽聽聽exclamEncountered聽=聽FALSE;聽//聽聽聽聽聽聽聽and聽switch聽states<br />聽聽聽}</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><br /><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"><i>(text box continues on next page)</i></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_270.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_271</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_272.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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