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Chapter3_OOD
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ShapeArea
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ShapeArea_main.m
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1995-06-12
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#import <appkit/appkit.h>
#import "Rectangle.h"
#import "Square.h"
// a program that demonstrates dynamic binding
// function prototypes
void createObjects(void), run(void);
void calculateAreas(void), freeAll(void);
void main(void);
BOOL readInput(void);
// global variable
id theList;
void createObjects(void)
{
// create list to hold shapes
theList = [[List alloc] init];
}
void run(void)
{
// stay in loop until Q is pressed
BOOL done = NO;
while (!done)
{
done = readInput();
}
}
BOOL readInput(void)
{
char inputString[10];
unsigned int choice;
float width, height;
id object;
// print the menu
printf("\nShapeArea calculates the ");
printf("areas of various shapes\n");
printf("==============\n");
printf("Select a shape\n");
printf("Type Q to quit\n\n");
printf("1 rectangle\n");
printf("2 square\n");
printf("===============\n");
// get input
scanf("%s", inputString);
if (strcmp(inputString, "Q") != 0)
{
choice = atoi(inputString);
switch (choice)
{
case 1:
// get width and height
printf("Enter the height\n");
scanf("%f", &height);
printf("Enter the width\n");
scanf("%f", &width);
// create rectangle and init it
object = [[Rectangle alloc]
initHeight:height
width:width];
// add rectangle to list
[theList addObject:object];
printf("The area of this shape is %.2f\n",
[object calcArea]);
break;
case 2:
// get height for square
printf("Enter the height\n");
// since a square's height
// is equal to its width,
// get only one value
scanf("%f", &height);
// create square and init it
object = [[Square alloc]
initHeight:height
width:height];
// add square to list
[theList addObject:object];
printf("The area of this shape is %.2f\n",
[object calcArea]);
break;
default:
// invalid choice
printf("No such shape!\n");
printf("Please try again!\n\n");
break;
}
// return NO to stay in while loop
// of run() function
return NO;
}
else
// return YES to abort while loop
return YES;
}
void calculateAreas(void)
{
int i;
// traverse the list and request each
// instance to perform its calcArea method
// this demonstrates dynamic binding
// since it impossible to determine
// the class of each instance until runtime
for (i=0; i < [theList count]; i++)
{
printf("\nThis shape is an instance of %s\n",
[[theList objectAt:i] name]);
printf("The area of this shape is %.2f\n",
[[theList objectAt:i] calcArea]);
}
}
void freeAll(void)
{
// free the objects in the list
// freeObjects sends a free message
// to each object in the list
[theList freeObjects];
// free the list itself
[theList free];
}
void main(void)
{
createObjects();
run();
calculateAreas();
freeAll();
exit(0);
}