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<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 1
in 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 declaration
9: class Rectangle
10: {
11: public:
12: // constructors
13: Rectangle(USHORT width, USHORT height);
14: ~Rectangle();
15:
16: // accessors
17: 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. methods
24: void DrawShape() const;
25:
26: private:
27: USHORT itsWidth;
28: USHORT itsHeight;
29: };
30:
31: // Class method implementations
32: 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 10,20
55: 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 switch
97: } // end while
98: } // end main
99:
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) Quit
1
******************************
******************************
******************************
******************************
******************************
*** Menu ***
(1) Draw Rectangle
(2) Area
(3) Perimeter
(4) Resize
(5) Quit
2
Area: 150
*** Menu ***
(1) Draw Rectangle
(2) Area
(3) Perimeter
(4) Resize
(5) Quit
3
Perimeter: 70
*** Menu ***
(1) Draw Rectangle
(2) Area
(3) Perimeter
(4) Resize
(5) Quit
4
New Width: 10
New height: 8
**********
**********
**********
**********
**********
**********
**********
**********
*** Menu ***
(1) Draw Rectangle
(2) Area
(3) Perimeter
(4) Resize
(5) Quit
2
Area: 80
*** Menu ***
(1) Draw Rectangle
(2) Area
(3) Perimeter
(4) Resize
(5) Quit
3
Perimeter: 36
*** Menu ***
(1) Draw Rectangle
(2) Area
(3) Perimeter
(4) Resize
(5) Quit
5
Exiting...
</FONT></PRE>
<P><FONT COLOR="#000077"><B>Analysis: </B></FONT>This program utilizes most of the
skills 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 on
the work you've done this week.<BR>
The first six lines set up the new types and definitions that will be used throughout
the program.</P>
<P>Lines 9-29 declare the <TT>Rectangle</TT> class. There are public accessor methods
for obtaining and setting the width and height of the rectangle, as well as for computing
the area and perimeter. Lines 32-43 contain the class function definitions that were
not 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, determine
its 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 menu
loop continues. The flag is only set to <TT>TRUE</TT> if the user picks Quit from
the menu.</P>
<P>Each of the other choices, with the exception of <TT>ChangeDimensions</TT>, calls
out 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," and
Day 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 cleaner
and 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 menu
to 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 in
debugging. 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 understand
sophisticated C++ programs. Of course, there's much more to do, and next week starts
with one of the most difficult concepts in C++: pointers. Don't give up now, you're
about to delve deeply into the meaning and use of object-oriented programming, virtual
functions, 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 page
to start Week 2.</P>
<P ALIGN="CENTER"><BR>
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