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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_525</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_524.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_525</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_526.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 525</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">Notice that the value returned by each function is just the original character if the condition is not met. For example, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">tolower(M)</font><font face="Times New Roman, Times, Serif" size="3"> returns the character m, whereas </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">tolower(+)</font><font face="Times New Roman, Times, Serif" size="3"> 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">A common use of these two functions is to let the user respond to certain input prompts by using either uppercase or lowercase letters. For example, if you want to allow either <i>Y</i> or <i>y</i> for a Yes response from the user, and either <i>N</i> or <i>n</i> for No, you might do this:</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">cout聽<聽Enter聽Y聽or聽N:聽;<br />cin聽>>聽inputChar;<br />if聽(toupper(inputChar)聽==聽Y)<br />{<br />聽聽聽聽.<br />聽聽聽聽.<br />聽聽聽聽.<br /><br />}<br />else聽if聽(toupper(inputChar)聽==聽N)<br />{<br />聽聽聽聽.<br />聽聽聽聽.<br />聽聽聽聽.<br /><br />}<br />else<br />聽聽聽聽PrintErrorMsg();</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">Below is a function named </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">Lower</font><font face="Times New Roman, Times, Serif" size="3">, which is our implementation of the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">tolower</font><font face="Times New Roman, Times, Serif" size="3"> function. (You wouldn't actually want to waste time by writing this function because </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">tolower</font><font face="Times New Roman, Times, Serif" size="3"> is already available to you.) This function returns the lowercase equivalent of an uppercase letter. In ASCII, each lowercase letter is exactly 32 positions beyond the corresponding uppercase letter. And in EBCDIC, the lowercase letters are 64 positions <i>before</i> their corresponding uppercase letters. To make our </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">Lower</font><font face="Times New Roman, Times, Serif" size="3"> function work on both ASCII-based and EBCDIC-based machines, we define a constant </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">DISTANCE</font><font face="Times New Roman, Times, Serif" size="3"> to have the value</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">a聽-聽A</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 ASCII, the value of this expression is 32. In EBCDIC, the value is 64.</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">#include聽<ctype.h>聽聽聽聽//聽For聽isupper()<br />聽聽.<br />聽聽.<br />聽聽.<br />char聽Lower(聽/*聽in聽*/聽char聽ch聽)<br /><br />//聽Postcondition:<br /></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_524.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_525</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_526.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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