OC5_类别

//
//  NSString+Reverse.h
//  OC5_类别
//
//  Created by zhangxueming on 15/6/16.
//  Copyright (c) 2015年 zhangxueming. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NSString (Reverse)

+ (NSString *)reverseString:(NSString *)aString;
+ (void)printString:(NSString *)aString;

@end

//
//  NSString+Reverse.m
//  OC5_类别
//
//  Created by zhangxueming on 15/6/16.
//  Copyright (c) 2015年 zhangxueming. All rights reserved.
//

#import "NSString+Reverse.h"
//类名+类别名.h
//类名+类别名.m

@implementation NSString (Reverse)

+ (NSString *)reverseString:(NSString *)aString
{
    NSString *str = @"";
    NSInteger len = [aString length];
    for (NSInteger i=len-1; i>=0; i--) {
        str = [str stringByAppendingFormat:@"%C",[aString characterAtIndex:i]];
    }
    return str;
}

+ (void)printString:(NSString *)aString
{
    NSLog(@"%@", aString);
}

@end

//
//  main.m
//  OC5_类别
//
//  Created by zhangxueming on 15/6/16.
//  Copyright (c) 2015年 zhangxueming. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "NSString+Reverse.h"//使用类别中的方法, 必须包含对应的头文件

//NSString
//类别
//给类或者类族扩展方法
//但是不能扩展实例变量

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        [NSString printString:[NSString reverseString:@"hello world"]];
    }
    return 0;
}