用不同方法为国家名称排序（调用block变量实现）

 1 //
 2 //  main.m
 3 //  block的实际应用
 4 //
 5 //  Created by LongMa on 15/9/2.
 6 //  Copyright (c) 2015年 Dast. All rights reserved.
 7 //
 8
 9 #import <Foundation/Foundation.h>
10 #import "Countries.h"
11 int main(int argc, const char * argv[])
12 {
13     char* countries[] = {"Uk","Korean","China","Japan","Autralia","Vietnam","Germany"};
14     int length = sizeof(countries) / sizeof(countries[0]);
15     __block unsigned long num1;
16     __block unsigned long num2;
17
18     Countries *c1 = [Countries new];
19
20     NSLog(@"国家名称按长度排序如下：");
21     [c1 sortWithCountries:countries andLength: length withBlock:^BOOL(char *str1, char *str2)
22     {
23         num1 = strlen(str1);
24         num2 = strlen(str2);
25
26         //汗，放减法溢出，以后unsigned 类型做减法时，记得用int强转参与减法运算的数据。
27         return (int)num1 - (int)num2 > 0 ;
28     }];
29
30     [c1 showCountries:countries WithLength:length];
31
32     NSLog(@"国家名称按字典序排序如下：");
33     [c1 sortWithCountries:countries andLength: length withBlock:^BOOL(char *str1, char *str2)
34      {
35          return  strcmp(str1, str2) > 0;
36      }];
37      [c1 showCountries:countries WithLength:length];
38
39     return 0;
40 }

1 //
2 //  Countries.h
3
4 #import <Foundation/Foundation.h>
5 typedef BOOL(^cmpBlock) (char*,char*);
6 @interface Countries : NSObject
7 - (void)sortWithCountries:(char*[])countries andLength:(int)length withBlock:(cmpBlock)cmpB;
8 - (void)showCountries:(char*[])countries WithLength:(int)length ;
9 @end

 1 //
 2 //  Countries.m
 3
 4 #import "Countries.h"
 5 #import <string.h>//别忘了
 6
 7 @implementation Countries
 8
 9 //char* 后面必须有[],是字符指针数组，不是字符指针,而(char*)[]是指向数组的指针，不对！    cmpB：block变量，传入比较方法的代码
10 - (void)sortWithCountries:(char*[])countries andLength:(int)length withBlock:(cmpBlock)cmpB
11 {
12     for (int i = 0; i < length - 1; i++)//冒泡排序
13     {
14         for (int j = 0; j < length - 1 - i; j++)
15         {
16             //int res = strcmp(countries[j], countries[j + 1]);//在这换为block
17            BOOL res = cmpB(countries[j],countries[j + 1]);//block自定义的返回值为 BOOL
18             if (YES == res )
19             {
20                 char* temp = countries[j];
21                 countries[j] = countries[j + 1];
22                 countries[j +1] = temp;
23             }
24         }
25     }
26 }
27
28 - (void)showCountries:(char*[])countries WithLength:(int)length
29 {
30     for (int i = 0; i < length; i++)
31     {
32         NSLog(@"%s",countries[i]);
33     }
34 }
35 @end

运行结果如下：

ps：bug分析。unsigned long类型属性相减会溢出的问题，检查了好久，同桌和辅导员都没有解决！最后自己不断验证才发现是溢出了，

　　　　　　以后遇见这种情况，做减法前都 强转为int 保证负数能正常得出。并用 int类型 变量接收或 与0比较后  用BOOL类型变量接收 即可！

　　验证图如下：