下面是是一个比较复杂的类。
定义一个四则运算计算器Caculator的接口和实现。
在main函数中，让用户输入四则运算表达式，比如a+b，a-b。
最后，在控制台输出结果。
用到的语法：接口、类的定义，实例方法，switch-case语句。
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/// main.m// switch-case//// Created by fansunion on 15/11/15.// Copyright (c) 2015年 demo. All rights reserved.//#import <Foundation/Foundation.h>@interface Caculator : NSObject-(void)setValue:(double)value;-(double)getResult;-(void)add:(double)value;-(void)sub:(double)value;-(void)multiply:(double)value;-(void)divide:(double)value;@end@implementation Caculator{double value;}-(void)setValue:(double)v{value=v;}-(void)add:(double)v{value+=v;}-(void)sub:(double)v{value-=v;}-(void)multiply:(double)v{value*=v;}-(void)divide:(double)v{value/= v;}-(double)getResult{return value;}@endint main(int argc, const char * argv[]) {@autoreleasepool {double value = 0;double v=0;char operator;Caculator *caculator =[[Caculator alloc]init];NSLog(@"请输入表达式!");scanf("%lf %c %lf",&value,&operator,&v);[caculator setValue:value];switch(operator){case ‘+’:[caculator add:v];break;case ‘-‘:[caculator sub:v];break;case ‘*’:[caculator multiply:v];break;case ‘/’:[caculator divide:v];break;default:NSLog(@"未知的操作符");break;}NSLog(@"%.2f",[caculator getResult]);}return 0;}
加法，2015+2014=4029
2015-11-15 17:23:13.722 switch-case[1684:89106] 请输入表达式!
2015+2014
2015-11-15 17:23:21.586 switch-case[1684:89106] 4029.00
Program ended with exit code: 0
减法，2015-2020=-5
2015-11-15 17:23:44.579 switch-case[1688:89497] 请输入表达式!
2015-2020
2015-11-15 17:23:55.500 switch-case[1688:89497] -5.00
Program ended with exit code: 0
乘法，2015*10=20150
2015-11-15 17:24:35.764 switch-case[1692:89985] 请输入表达式!
2015*10
2015-11-15 17:24:45.414 switch-case[1692:89985] 20150.00
Program ended with exit code: 0
除法，2015/10=201.5
2015-11-15 17:24:58.379 switch-case[1696:90264] 请输入表达式!
2015/10
2015-11-15 17:25:10.669 switch-case[1696:90264] 201.50
Program ended with exit code: 0
学习这个例子，感觉瞬间回到了2008年上半学年，大一上学期～
生命不是一场赛跑，而是一次旅行。比赛在乎终点，而旅行在乎沿途风景。
