类目（分类）

#import <Foundation/Foundation.h>

@interface NSString (Reverse)

-(NSString *)reverse;

@end

#import "NSString+Reverse.h"

@implementation NSString (Reverse)

-(NSString *)reverse
{
    NSMutableString *str =[NSMutableString string];
    //  小于字符串的长度
    for (int i=(int)self.length-1; i>=0; i--) {
        // 字符串的倒序
        char ch=[self characterAtIndex:i];
        // 字符串的添加
        [str appendFormat:@"%c",ch];
    }
    return str;
}
@end

#import <Foundation/Foundation.h>

@interface NSString (Catel)
-(NSNumber *)lengthAsString;
@end

#import "NSString+Catel.h"

@implementation NSString (Catel)
-(NSNumber *)lengthAsString
{
    int len= (int)self.length;
    return [NSNumber numberWithInt:len];
}
@end

#import <Foundation/Foundation.h>
#import "NSString+Reverse.h"
#import "NSString+Catel.m"
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSString *str =@"abc";
        // 逆序输出
        NSLog(@"%@",[str reverse]);
        
        NSLog(@"%d",[str lengthAsString].intValue);
    }
    return 0;
}

#import <Foundation/Foundation.h>

@interface NSArray (Reversre)
-(NSArray *)reverse;
@end

#import "NSArray+Reversre.h"

@implementation NSArray (Reversre)
-(NSArray *)reverse  //  逆序输出方法实现
{
    NSMutableArray *array=[NSMutableArray array];
    // 小于集合的个数
    for (int i=(int)self.count-1; i>=0; i--) {
        // 集合的添加用addObject  集合的倒序objectAtIndex
        [array addObject:[self objectAtIndex:i]];
    }
    return  array;
}
@end

#import <Foundation/Foundation.h>
#import "NSArray+Reversre.h"
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        //  不可变集合的初始化
        NSArray *array=[NSArray arrayWithObjects:@"a",@"b",@"c",@"d",@"e", nil];
      NSArray *arr=[array reverse];
        NSLog(@"%@",arr);
    }
    return 0;
}