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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_945</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_944.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_945</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_946.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 945</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">In Chapter 12, we introduced the notion of a list as an ADT. At various times, we have talked about typical list operations: insert an item into the list, delete an item, report whether the list is full, report whether the list is empty, search for a particular item, sort the list items into order, print the entire list, and so forth. Shouldn't we include all these operations when designing our list of time cards? Probably not. It's unlikely that a list of time cards would be considered general-purpose enough to warrant the effort. Let's stick to the operations we listed in the object table:</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">Read all time cards into the list</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">Look up time card information</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">To choose a data representation for the list, let's review the relationships among the objects in our program. We said that the time card list object is composed of time card objects. Therefore, we can use a 500-element array of </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">TimeCard</font><font face="Times New Roman, Times, Serif" size="3"> class objects to represent the list. Because we'll be searching the array for time card information, the data representation should also include an integer variable indicating the length of the list (the number of array elements that are actually in use).</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">Before we write the specification of the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">TimeCardList</font><font face="Times New Roman, Times, Serif" size="3"> class, let's review the operations once more. The lookup operation must search the array for a particular time card. Because the array is potentially very large (500 elements), a binary search is better than a sequential search. However, a binary search requires the array elements to be in sorted order. We must either insert each time card into its proper place as it is read from the data file or sort the time cards after they have been read. Let's take the latter approach and add another operationa sorting operation. (We'll use the selection sort we developed in Chapter 12.) Finally, we need one more operation to initialize the private data: a class constructor. Here is the resulting class specification:</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">//******************************************************************<br />//聽SPECIFICATION聽FILE聽(tclist.h)<br />//聽This聽file聽gives聽the聽specification聽of聽TimeCardList,聽an聽ADT聽for聽a<br />//聽list聽of聽TimeCard聽objects.<br />//******************************************************************<br />#ifndef聽TCLIST_H<br />#define聽TCLIST_H<br /><br />#include聽timecard.h<br />#include聽bool.h<br />#include聽<fstream.h><br /><br />const聽int聽MAX_LENGTH聽=聽500;聽聽聽//聽Maximum聽number聽of聽time聽cards<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_944.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_945</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_946.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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