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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_333</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_332.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_333</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_334.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 333</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">parameters. (Some programmers use the terms <i>actual argument</i> and <i>formal argument</i> instead of <i>actual parameter</i> and <i>formal parameter.</i> Others use the term <i>argument</i> in place of <i>actual parameter,</i> and <i>parameter</i> in place of <i>formal parameter.)</i></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" width="100%"><tr><td rowspan="5"><img src="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" border="0" width="96" height="1" alt="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" border="0" width="96" height="1" alt="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" /></td></tr><tr><td colspan="3" height="2"><table cellpadding="0" cellspacing="0" border="0"><tr><td></td></tr></table></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Formal Parameter A variable declared in a function heading.</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" width="100%"><tr><td rowspan="5"><img src="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" border="0" width="96" height="1" alt="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" border="0" width="96" height="1" alt="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Actual Parameter A variable or expression listed in a call to a function.</font></td><td></td></tr><tr><td colspan="3" height="2"><table cellpadding="0" cellspacing="0" border="0"><tr><td></td></tr></table></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 the NewWelcome program, the actual parameters in the two function calls are the constants 2 and 4, and the formal parameter in the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">PrintLines</font><font face="Times New Roman, Times, Serif" size="3"> function is named </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">numLines</font><font face="Times New Roman, Times, Serif" size="3">. The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">main</font><font face="Times New Roman, Times, Serif" size="3"> function first calls </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">PrintLines</font><font face="Times New Roman, Times, Serif" size="3"> with an actual parameter of 2. When control is turned over to </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">PrintLines</font><font face="Times New Roman, Times, Serif" size="3">, the formal parameter </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">numLines</font><font face="Times New Roman, Times, Serif" size="3"> is initialized to 2. Within </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">PrintLInes</font><font face="Times New Roman, Times, Serif" size="3">, the countcontrolled loop executes twice and the function returns. The second time </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">PrintLines</font><font face="Times New Roman, Times, Serif" size="3"> is called, the formal parameter </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">numLines</font><font face="Times New Roman, Times, Serif" size="3"> is initialized to the value of the actual parameter, 4. The loop executes four times, after which the function returns.</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">Although there is no benefit in doing so, we could write the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">main</font><font face="Times New Roman, Times, Serif" size="3"> function this way:</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">int聽main()<br />{<br />聽聽聽聽int聽lineCount;<br /><br />聽聽聽聽lineCount聽=聽2;<br />聽聽聽聽PrintLines(lineCount);<br />聽聽聽聽cout聽<<聽聽Welcome聽Home!聽<<聽endl;<br />聽聽聽聽lineCount聽=聽4;<br />聽聽聽聽PrintLines(lineCount);<br />聽聽聽聽return聽0;<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">In this version, the actual parameter in each call to </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">PrintLines</font><font face="Times New Roman, Times, Serif" size="3"> is a variable rather than a constant. Each time </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">main</font><font face="Times New Roman, Times, Serif" size="3"> calls </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">PrintLines</font><font face="Times New Roman, Times, Serif" size="3">, a copy of the actual parameter's value is passed to the function to initialize the formal parameter </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">numLines</font><font face="Times New Roman, Times, Serif" size="3">. This version shows that when you pass a variable as an actual parameter, the actual and formal parameters can have different names.</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 NewWelcome program brings up a second major reason for using functionsnamely, a function can be called from many places in the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">main</font><font face="Times New Roman, Times, Serif" size="3"> function (or from other functions). Use of multiple calls can save a great</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_332.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_333</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_334.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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