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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><HTML><HEAD><!-- This document was created from RTF source by rtftohtml version 3.0.1 --> <META NAME="GENERATOR" Content="Symantec Visual Page 1.0"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html;CHARSET=iso-8859-1"> <TITLE>Teach Yourself C++ in 21 Days</TITLE></HEAD><BODY TEXT="#000000" BGCOLOR="#FFFFFF"><H1></H1><P ALIGN="CENTER"><A HREF="ch07.htm" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/htm/ch07.htm"><IMG SRC="BLANPREV.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANPREV.GIF"WIDTH="37" HEIGHT="37" ALIGN="BOTTOM" BORDER="0"></A><A HREF="tppmsgs/msgs0.htm#1" tppabs="http://www.mcp.com/sams"><IMGSRC="BLANHOME.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANHOME.GIF" WIDTH="37" HEIGHT="37" ALIGN="BOTTOM"BORDER="0"></A><A HREF="index.htm" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/index.htm"><IMG SRC="BLANTOC.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANTOC.GIF"WIDTH="37" HEIGHT="37" ALIGN="BOTTOM" BORDER="0"></A><A HREF="ch08.htm" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/htm/ch08.htm"><IMG SRC="BLANNEXT.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANNEXT.GIF"WIDTH="37" HEIGHT="37" ALIGN="BOTTOM" BORDER="0"></A><H2 ALIGN="CENTER"><BR><A NAME="Heading1"></A><FONT COLOR="#000077">In Review</FONT></H2><P><A NAME="Heading2"></A><FONT SIZE="4" COLOR="#000077"><B>Listing R1.1. Week 1in Review listing.</B></FONT><FONT COLOR="#0066FF"></FONT><PRE><FONT COLOR="#0066FF">1: #include <iostream.h>2:3: typedef unsigned short int USHORT;4: typedef unsigned long int ULONG;5: enum BOOL { FALSE, TRUE};6: enum CHOICE { DrawRect = 1, GetArea, 7: GetPerim, ChangeDimensions, Quit};8: // Rectangle class declaration9: class Rectangle10: {11: public:12: // constructors13: Rectangle(USHORT width, USHORT height);14: ~Rectangle();15:16: // accessors17: USHORT GetHeight() const { return itsHeight; }18: USHORT GetWidth() const { return itsWidth; }19: ULONG GetArea() const { return itsHeight * itsWidth; }20: ULONG GetPerim() const { return 2*itsHeight + 2*itsWidth; }21: void SetSize(USHORT newWidth, USHORT newHeight);22:23: // Misc. methods24: void DrawShape() const;25:26: private:27: USHORT itsWidth;28: USHORT itsHeight;29: };30:31: // Class method implementations32: void Rectangle::SetSize(USHORT newWidth, USHORT newHeight)33: {34: itsWidth = newWidth;35: itsHeight = newHeight;36: }37:38:39: Rectangle::Rectangle(USHORT width, USHORT height)40: {41: itsWidth = width;42: itsHeight = height;43: }44:45: Rectangle::~Rectangle() {}46:47: USHORT DoMenu();48: void DoDrawRect(Rectangle);49: void DoGetArea(Rectangle);50: void DoGetPerim(Rectangle);51:52: void main ()53: {54: // initialize a rectangle to 10,2055: Rectangle theRect(30,5);56:57: USHORT choice = DrawRect;58: USHORT fQuit = FALSE;59:60: while (!fQuit)61: {62: choice = DoMenu();63: if (choice < DrawRect || choice > Quit)64: {65: cout << "\nInvalid Choice, please try again.\n\n";66: continue;67: }68: switch (choice)69: {70: case DrawRect:71: DoDrawRect(theRect);72: break;73: case GetArea:74: DoGetArea(theRect);75: break;76: case GetPerim:77: DoGetPerim(theRect);78: break;79: case ChangeDimensions:80: USHORT newLength, newWidth;81: cout << "\nNew width: ";82: cin >> newWidth;83: cout << "New height: ";84: cin >> newLength;85: theRect.SetSize(newWidth, newLength);86: DoDrawRect(theRect);87: break;88: case Quit:89: fQuit = TRUE;90: cout << "\nExiting...\n\n";91: break;92: default:93: cout << "Error in choice!\n";94: fQuit = TRUE;95: break;96: } // end switch97: } // end while98: } // end main99:100:101: USHORT DoMenu()102: {103: USHORT choice;104: cout << "\n\n *** Menu *** \n";105: cout << "(1) Draw Rectangle\n";106: cout << "(2) Area\n";107: cout << "(3) Perimeter\n";108: cout << "(4) Resize\n";109: cout << "(5) Quit\n";110:111: cin >> choice;112: return choice;113: }114:115: void DoDrawRect(Rectangle theRect)116: {117: USHORT height = theRect.GetHeight();118: USHORT width = theRect.GetWidth();119:120: for (USHORT i = 0; i<height; i++)121: {122: for (USHORT j = 0; j< width; j++)123: cout << "*";124: cout << "\n";125: }126: }127:128:129: void DoGetArea(Rectangle theRect)130: {131: cout << "Area: " << theRect.GetArea() << endl;132: }133:134: void DoGetPerim(Rectangle theRect)135: {136: cout << "Perimeter: " << theRect.GetPerim() << endl;<TT>137: }</TT>Output: *** Menu ***(1) Draw Rectangle(2) Area(3) Perimeter(4) Resize(5) Quit1****************************************************************************************************************************************************** *** Menu ***(1) Draw Rectangle(2) Area(3) Perimeter(4) Resize(5) Quit2Area: 150 *** Menu ***(1) Draw Rectangle(2) Area(3) Perimeter(4) Resize(5) Quit3Perimeter: 70 *** Menu ***(1) Draw Rectangle(2) Area(3) Perimeter(4) Resize(5) Quit4New Width: 10New height: 8******************************************************************************** *** Menu ***(1) Draw Rectangle(2) Area(3) Perimeter(4) Resize(5) Quit2Area: 80 *** Menu ***(1) Draw Rectangle(2) Area(3) Perimeter(4) Resize(5) Quit3Perimeter: 36 *** Menu ***(1) Draw Rectangle(2) Area(3) Perimeter(4) Resize(5) Quit5Exiting...</FONT></PRE><P><FONT COLOR="#000077"><B>Analysis: </B></FONT>This program utilizes most of theskills you learned this week. You should not only be able to enter, compile, link,and run this program, but also understand what it does and how it works, based onthe work you've done this week.<BR>The first six lines set up the new types and definitions that will be used throughoutthe program.</P><P>Lines 9-29 declare the <TT>Rectangle</TT> class. There are public accessor methodsfor obtaining and setting the width and height of the rectangle, as well as for computingthe area and perimeter. Lines 32-43 contain the class function definitions that werenot declared inline.</P><P>The function prototypes, for the non-class member functions, are on lines 47-50,and the program begins on line 52. The essence of this program is to generate a rectangle,and then to print out a menu offering five options: Draw the rectangle, determineits area, determine its perimeter, resize the rectangle, or quit.</P><P>A flag is set on line 58, and when that flag is not set to <TT>TRUE</TT> the menuloop continues. The flag is only set to <TT>TRUE</TT> if the user picks Quit fromthe menu.</P><P>Each of the other choices, with the exception of <TT>ChangeDimensions</TT>, callsout to a function. This makes the <TT>switch</TT> statement cleaner. <TT>ChangeDimensions</TT>cannot call out to a function because it must change the dimensions of the rectangle.If the rectangle were passed (by value) to a function such as <TT>DoChangeDimensions()</TT>,the dimensions would be changed on the local copy of the rectangle in <TT>DoChangeDimensions()</TT>and not on the rectangle in <TT>main()</TT>. On Day 8, "Pointers," andDay 10, "Advanced Functions," you'll learn how to overcome this restriction,but for now the change is made in the <TT>main()</TT> function.</P><P>Note how the use of an enumeration makes the <TT>switch</TT> statement much cleanerand easier to understand. Had the <TT>switch</TT> depended on the numeric choices(1-5) of the user, you would have to constantly refer to the description of the menuto see which pick was which.</P><P>On line 63, the user's choice is checked to make sure it is in range. If not,an error message is printed and the menu is reprinted. Note that the <TT>switch</TT>statement includes an "impossible" default condition. This is an aid indebugging. If the program is working, that statement can never be reached.<H3 ALIGN="CENTER"><A NAME="Heading3"></A><FONT COLOR="#000077">Week in Review</FONT></H3><P>Congratulations! You've completed the first week! Now you can create and understandsophisticated C++ programs. Of course, there's much more to do, and next week startswith one of the most difficult concepts in C++: pointers. Don't give up now, you'reabout to delve deeply into the meaning and use of object-oriented programming, virtualfunctions, and many of the advanced features of this powerful language.</P><P>Take a break, bask in the glory of your accomplishment, and then turn the pageto start Week 2.</P><P ALIGN="CENTER"><BR><BR><A HREF="ch07.htm" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/htm/ch07.htm"><IMG SRC="BLANPREV.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANPREV.GIF" WIDTH="37"HEIGHT="37" ALIGN="BOTTOM" BORDER="0"></A><A HREF="tppmsgs/msgs0.htm#1" tppabs="http://www.mcp.com/sams"><IMGSRC="BLANHOME.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANHOME.GIF" WIDTH="37" HEIGHT="37" ALIGN="BOTTOM"BORDER="0"></A><A HREF="index.htm" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/index.htm"><IMG SRC="BLANTOC.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANTOC.GIF"WIDTH="37" HEIGHT="37" ALIGN="BOTTOM" BORDER="0"></A><A HREF="ch08.htm" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/htm/ch08.htm"><IMG SRC="BLANNEXT.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANNEXT.GIF"WIDTH="37" HEIGHT="37" ALIGN="BOTTOM" BORDER="0"></A><A HREF="#heading1"><IMG SRC="BLANTOP.GIF" tppabs="http://www.mcp.com/814147200/0-672/0-672-31070-8/buttons/BLANTOP.GIF"WIDTH="37" HEIGHT="37" ALIGN="BOTTOM" BORDER="0"></A></BODY></HTML>⌨️ 快捷键说明
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