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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_328</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_327.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_328</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_329.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 328</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="Courier New, Courier, Mono New, Courier, Mono" size="2">{<br />聽聽聽聽cout聽<<聽***************聽<<聽endl;<br />聽聽聽聽cout聽<<聽***************聽<<聽endll;<br />}<br /><br />//******************************************************************<br /><br />void聽Print4Lines()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Function聽heading<br /><br />//聽This聽function聽prints聽four聽lines聽of聽asterisks<br /><br />{<br />聽聽聽聽cout聽<<聽***************聽<<聽endl;<br />聽聽聽聽cout聽<<聽***************聽<<聽endl;<br />聽聽聽聽cout聽<<聽***************聽<<聽endl;<br />聽聽聽聽cout聽<<聽***************聽<<聽endl;<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">C++ function definitions can appear in any order. We could have chosen to place 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 last instead of first, but C++ programmers typically put </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">main</font><font face="Times New Roman, Times, Serif" size="3"> first and any supporting functions after it.</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 the Welcome program, the two statements just before 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 are called <i>function prototypes.</i> These declarations are necessary because of the C++ rule requiring you to declare an identifier before you can use it. Our </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">main</font><font face="Times New Roman, Times, Serif" size="3"> function uses the identifiers </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">Print2Lines</font><font face="Times New Roman, Times, Serif" size="3"> and </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">Print4Lines</font><font face="Times New Roman, Times, Serif" size="3">, but the definitions of those functions don't appear until later. We must supply the function prototypes to inform the compiler in advance that </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">Print2Lines</font><font face="Times New Roman, Times, Serif" size="3"> and </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">Print4Lines</font><font face="Times New Roman, Times, Serif" size="3"> are the names of functions, that they do not return function values, and that they have no parameters. We say more about function prototypes later in the chapter.</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">Because the Welcome program is so simple to begin with, it may seem more complicated with its modules written as functions. However, it is clear that it much more closely resembles our top-down design. This is especially true of 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. If you handed this code to someone, the person could look at 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 (which, as we said, usually appears first) and tell you immediately what the program doesit prints two lines of something, prints Welcome Home!, and prints four lines of something. If you asked the person to be more specific, he or she could then look up the details in the other function definitions. The person is able to begin with a top-level view of the program and then study the lower-level modules as necessary, without having to read the entire program or look at a module structure chart. As our programs grow to include many modules nested several levels deep, the ability to read a program in the same manner as a topdown design greatly aids in the development and debugging process.</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_327.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_328</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_329.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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