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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_413</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_412.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_413</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_414.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 413</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">聽聽聽聽return聽(fabs(angle1聽+聽angle2聽+聽angle3聽-聽180.0)聽<聽0.00000001);<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">The following program fragment shows how function </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">IsTriangle</font><font face="Times New Roman, Times, Serif" size="3"> might be called:</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">cin聽>>聽angleA聽>>聽angleB聽>>聽angleC;<br />if聽(IsTriangle(angleA,聽angleB,聽angleC))聽聽聽聽聽聽聽聽聽聽聽聽聽//聽Function聽call<br />聽聽聽聽cout聽<<聽The聽three聽angles聽form聽a聽valid聽triangle.;<br />else<br />聽聽聽聽cout聽<<聽Those聽angles聽do聽not聽form聽a聽triangle.;</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 If statement is much easier to understand with the function than it would be if the entire condition were coded directly. When a conditional test is at all complicated, a Boolean function is in order.</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 C++ standard library provides a number of helpful Boolean functions that let you test the contents of </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">char</font><font face="Times New Roman, Times, Serif" size="3"> variables. To use them, you </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">#include</font><font face="Times New Roman, Times, Serif" size="3"> the header file </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">ctype.h</font><font face="Times New Roman, Times, Serif" size="3">. Here are some of the available functions; Appendix C contains a more complete list.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table cellpadding="0" cellspacing="0" border="0" width="100%"><tr><td height="12"></td></tr><tr><td><table cellspacing="0" width="672" cellpadding="7"><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2"><i>Header File</i></font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2"><i>Function</i></font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2"><i>Function Type</i></font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2"><i>Function Value</i></font></td></tr><tr><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2"><ctype.h></font></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">isalpha(ch)</font></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">int</font></td></tr></table></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Nonzero, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">ch</font><font face="Times New Roman, Times, Serif" size="2"> is a letter (A,Z, az);<br />0, otherwise</font></td></tr><tr><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2"><ctype.h></font></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">isalnum(ch)</font></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">int</font></td></tr></table></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Nonzero, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">ch</font><font face="Times New Roman, Times, Serif" size="2"> is a letter or a digit (AZ, az, 09);<br />0, otherwise</font></td></tr><tr><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2"><ctype.h></font></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">isdigit(ch)</font></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">int</font></td></tr></table></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Nonzero, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">ch</font><font face="Times New Roman, Times, Serif" size="2"> is a digit (09);<br />0, otherwise</font></td></tr><tr><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2"><cytpe.h></font></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">islower(ch)</font></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">int</font></td></tr></table></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Nonzero, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">ch</font><font face="Times New Roman, Times, Serif" size="2"> is a lowercase letter (az);<br />0, otherwise</font></td></tr><tr><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2"><ctype.h></font></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">isspace(ch)</font></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">int</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" border="0" width="0" height="1" alt="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" /></td> <td colspan="3" height="1"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Nonzero, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">ch</font><font face="Times New Roman, Times, Serif" size="2"> is a whitespace character (blank, newline, tab, carriage return, form feed);</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">0, otherwise</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"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2"><ctype.h></font></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">isupper(ch)</font></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">int</font></td></tr></table></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Nonzero, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">ch</font><font face="Times New Roman, Times, Serif" size="2"> is an uppercase letter (AZ);<br />0, otherwise</font></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">Although Boolean is not a built-in data type in C++, the is functions behave like Boolean functions. They return an </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">int</font><font face="Times New Roman, Times, Serif" size="3"> value that is nonzero (true) or zero (false). These functions are convenient to use and make programs more readable. For example, the test</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">if聽(isalnum(inputChar))</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_412.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_413</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_414.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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