从零开始学习Object-C---第四天（3）

今天首先是总结之前的数据类型：

注：id数据类型是OC的一种特殊的数据类型，可用来存储任何数据类型，是多态和动态绑定的基础。

开始新的讲解－－算术表达式

一段代码开始今天的学习：

 1 //
 2 //  main.m
 3 //  Demo5
 4 //
 5 //  Created by lee on 14/11/6.
 6 //  Copyright (c) 2014年 lee. All rights reserved.
 7 //
 8
 9 #import <Foundation/Foundation.h>
10
11 int main(int argc, const char * argv[]) {
12     @autoreleasepool {
13         int a = 100;
14         int b = 2;
15         int c = 25;
16         int d = 4;
17         int result;
18         result = a-b;
19         NSLog(@"a - b = %i", result);
20
21         result = b * c;
22         NSLog(@"b * c = %i", result);
23
24         result = a / c;
25         NSLog(@"a / c = %i", result);
26
27         result = a + b * c;
28         NSLog(@"a + b * c = %i", result);
29
30         result = a * b + c * d;
31         NSLog(@"a * b + c * d = %i", result);
32     }
33     return 0;
34 }
35 输出结果：
36 2014-11-06 01:16:40.458 Demo5[651:34029] a - b = 98
37 2014-11-06 01:16:40.458 Demo5[651:34029] b * c = 50
38 2014-11-06 01:16:40.458 Demo5[651:34029] a / c = 4
39 2014-11-06 01:16:40.459 Demo5[651:34029] a + b * c = 150
40 2014-11-06 01:16:40.459 Demo5[651:34029] a * b + c * d = 300
41 Program ended with exit code: 0

注：OC中算法优先级和其他语言的优先级相同，先乘除后加减，括号能改变计算顺序

运用算数表达式的规则写出计算器类，来实现基本的算术：

首先定义接口：包含 初始化(clear)，get set方法，加(add)减(subtract)乘(mutiply)除(devide)方法定义

 1 //
 2 //  NSObject+Calculator.h
 3 //  Demo5
 4 //
 5 //  Created by lee on 14/11/6.
 6 //  Copyright (c) 2014年 lee. All rights reserved.
 7 //
 8
 9 #import <Foundation/Foundation.h>
10
11 @interface Calculator : NSObject
12 {
13     double accumulator;
14 }
15 //accmulator
16 -(void) setAccumulator: (double) value;
17 -(void) clear;
18 -(double) getAccumulator;
19
20 //arithetic methods
21 -(void) add: (double) value;
22 -(void) subtract: (double) value;
23 -(void) multiply: (double) value;
24 -(void) devide: (double) value;
25 @end

然后定义实现类，实现接口中定义的方法

 1 //
 2 //  NSObject+Calculator.m
 3 //  Demo5
 4 //
 5 //  Created by lee on 14/11/6.
 6 //  Copyright (c) 2014年 lee. All rights reserved.
 7 //
 8
 9 #import "NSObject+Calculator.h"
10
11 @implementation Calculator
12 -(void) setAccumulator:(double)value
13 {
14     accumulator = value;
15 }
16
17 -(void) clear
18 {
19     accumulator = 0;
20 }
21
22  -(double) getAccumulator
23 {
24     return accumulator;
25 }
26
27 -(void) add:(double)value
28 {
29     accumulator += value;
30 }
31
32 -(void) subtract:(double)value
33 {
34     accumulator -= value;
35 }
36
37 -(void) multiply:(double)value
38 {
39     accumulator *= value;
40 }
41
42 -(void) devide:(double)value
43 {
44     accumulator /= value;
45 }
46
47 @end

最后方法调用以及输出结果

 1 //
 2 //  main.m
 3 //  Demo5
 4 //
 5 //  Created by lee on 14/11/6.
 6 //  Copyright (c) 2014年 lee. All rights reserved.
 7 //
 8
 9 #import <Foundation/Foundation.h>
10 #import "NSObject+Calculator.h"
11
12 int main(int argc, const char * argv[]) {
13     @autoreleasepool {
14         Calculator *deskCalc;
15         deskCalc = [[Calculator alloc] init];
16
17         [deskCalc clear];
18         [deskCalc setAccumulator: 10];
19         NSLog(@"The result id %g", [deskCalc getAccumulator]);
20         [deskCalc add: 200];
21         NSLog(@"The result id %g", [deskCalc getAccumulator]);
22         [deskCalc devide: 15.0];
23         NSLog(@"The result id %g", [deskCalc getAccumulator]);
24         [deskCalc subtract: 10.0];
25         NSLog(@"The result id %g", [deskCalc getAccumulator]);
26         [deskCalc multiply: 5];
27         NSLog(@"The result is %g", [deskCalc getAccumulator]);
28     }
29     return 0;
30 }
31 输出结果：
32 2014-11-06 00:50:19.874 Demo5[601:25952] The result id 10
33 2014-11-06 00:50:19.875 Demo5[601:25952] The result id 210
34 2014-11-06 00:50:19.875 Demo5[601:25952] The result id 14
35 2014-11-06 00:50:19.875 Demo5[601:25952] The result id 4
36 2014-11-06 00:50:19.875 Demo5[601:25952] The result is 20
37 Program ended with exit code: 0

类和方法定义和使用参考：http://www.cnblogs.com/likun-java/p/4058448.html