[学习笔记—Objective-C]《Objective-C 程序设计 第6版》第四章 数据类型和表达式 课后练习题 4-10

4-10 题目：
为代码清单 4-6中的Calculator添加一项存储功能。实现以下方法声明并实现它们：

-(double) memoryClear;                  -(double) memoryStore;                  -(double) memoryRecall;                -(double) memoryAdd: (double) value;    -(double) memorysubtract:(double) value; 

4-10 代码：

#import <Foundation/Foundation.h>@interface Calculator : NSObject//累加方法-(void) setAccumulator: (double) value;-(void) clear;-(double) accumulator;//算术方法-(void) add: (double) value;-(void) subtract: (double) value;-(void) multiply: (double) value;-(void) divide: (double) value;//内存功能-(double) memoryClear;                   //清理内存-(double) memoryStore;                   //设置内存为累加器-(double) memoryRecall;                  //设置累加器到内存-(double) memoryAdd: (double) value;     //添加值到内存-(double) memorysubtract:(double) value; //与内存的值相减@end@implementation Calculator{    double accumulator;    double memory;}-(void) setAccumulator:(double)value{    accumulator = value;}-(void) clear{    accumulator = 0;}-(double) accumulator{    return accumulator;}-(void) add: (double) value{    accumulator += value;}-(void) subtract: (double) value{    accumulator -= value;}-(void) multiply: (double) value{    accumulator  *= value;}-(void) divide: (double)value{    accumulator /= value;}//内存功能-(double) memoryClear{    memory = 0;    return accumulator;}-(double) memoryStore{    memory = accumulator;    return accumulator;}-(double) memoryRecall{    accumulator = memory;    return accumulator;}-(double) memoryAdd: (double) value{    memory += value;    return accumulator;}-(double) memorysubtract:(double) value{    memory -= value;    return accumulator;}@endint main(int argc, const char * argv[]){    @autoreleasepool {        Calculator *deskCalc = [[Calculator alloc] init];        [deskCalc setAccumulator:100.0];        [deskCalc add:200.];        [deskCalc divide:15.0];        [deskCalc subtract:10.0];        [deskCalc multiply:5];        NSLog(@"The result is %g", [deskCalc accumulator]);        [deskCalc memoryStore]; //累加器值添加到内存              [deskCalc memoryAdd:5]; //内存值+5               [deskCalc memoryRecall];//内存值添加到累加器                NSLog(@"The result is %g", [deskCalc accumulator]);        [deskCalc memorysubtract:10];//内存值-10                [deskCalc memoryRecall];     //内存值添加到累加器            NSLog(@"The result is %g", [deskCalc accumulator]);        [deskCalc memoryClear];  //内存值清零        [deskCalc memoryRecall]; //内存值添加到累加器        NSLog(@"The result is %g", [deskCalc accumulator]);  }    return 0;}

代码运行结果：

The result is 50
The result is 55
The result is 45
The result is 0