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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_233</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_232.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_233</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_234.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 233</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">The next step is to examine each module at level 1 and answer this question: If the level-2 modules (if any) are assumed to be correct, will this level1 module do what it is supposed to do? We simply repeat the walk-through process for each module, starting with its particular precondition. In this example, there are no level-2 modules, so the level-1 modules must be complete.</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">Get Data correctly reads in five values</font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">code</font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size1</font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size2</font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size3</font><font face="Times New Roman, Times, Serif" size="3">, and </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">numOrdered</font><font face="Times New Roman, Times, Serif" size="3">thereby satisfying its postcondition. (The next refinement is to code this instruction in C++. Whether it is coded correctly or not is <i>not</i> an issue in this phase; we deal with the code when we perform testing in the implementation phase.)</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">Calculate Lumber Amount assigns to variable </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">boardFeet</font><font face="Times New Roman, Times, Serif" size="3"> the result of multiplying the contents of </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size1</font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size2</font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size3</font><font face="Times New Roman, Times, Serif" size="3"> (itself multiplied by the literal 12), and </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">numOrdered</font><font face="Times New Roman, Times, Serif" size="3">, and dividing by </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">BOARD_FT_INCHES</font><font face="Times New Roman, Times, Serif" size="3">. That's the correct formula for computing board feet, so the step is correct and the calculated value is printed. Calculate Lumber Amount meets its required postcondition.</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">Calculate Plywood Amount assigns to the variable </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">fullSheets</font><font face="Times New Roman, Times, Serif" size="3"> the result of dividing </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size1</font><font face="Times New Roman, Times, Serif" size="3"> by </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size2</font><font face="Times New Roman, Times, Serif" size="3">, multiplying by </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">size3</font><font face="Times New Roman, Times, Serif" size="3"> (itself multiplied by the literal 12), </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">WIDTH_INCHES</font><font face="Times New Roman, Times, Serif" size="3">, and </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">numOrdered</font><font face="Times New Roman, Times, Serif" size="3">, and dividing by </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">PLYWOOD_INCHES</font><font face="Times New Roman, Times, Serif" size="3">. This is the correct formula for computing full sheets of plywood, so this step is correct and the calculated value is printed. Calculate Plywood Amount also meets its required postcondition.</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">Once we've completed the algorithm walk-through, we have to correct any discrepancies and repeat the process. When we know that the modules do what they are supposed to do, we start translating the top-down design into our programming language.</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">We need to fix the problem we discovered in the algorithmnamely, that the main module does not guarantee the required precondition for Calculate Plywood Amount. We have to change the main module so that the assertion </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">code</font><font face="Times New Roman, Times, Serif" size="3"> equals P is true before Calculate Plywood Amount is entered. Here's the revised main module:</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">Main聽Module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<i>Level聽0</i></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table cellspacing="0" border="0" width="288" cellpadding="4"><tr><td valign="top"><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">Get聽data<br />IF聽code聽equals聽L<br />聽聽聽聽Calculate聽lumber聽amount<br />IF聽code聽equals聽P<br />聽聽聽聽Calculate聽plywood聽amount</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></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">The main module now sees to it that data has been input to the five variables and that </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">code</font><font face="Times New Roman, Times, Serif" size="3"> contains the letter P before Calculate Plywood Amount is executed. This change corrects the problem we found in the walk-</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_232.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_233</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_234.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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