一个反向输出字符串的例子，不用componentsSeparatedByString去实现以空格字符分割字符串然后反向输出：

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{

@autoreleasepool {

// insert code here...
//NSLog(@"Hello, World!");
NSString *a =[[NSString alloc] initWithFormat:@"I am a good person\n"];
NSMutableString *letters = [NSMutableString stringWithFormat:@""];
//NSInteger t = 0;
for (NSInteger i = a.length-1;i>=0; i--)
{
if([a characterAtIndex:i]==' ')
{
NSString *temp = [a substringWithRange:NSMakeRange(i+1,a.length-i-1)];
//NSLog(@"%@",temp);
for(NSInteger j=0;j<temp.length;j++)
{
if([temp characterAtIndex:j]==' ' || [temp characterAtIndex:j]=='\n')
{NSString *temp2= [temp substringWithRange:NSMakeRange(0, j)];
[letters appendString:temp2];
[letters appendString:@" "];
//NSLog(@"%@",temp2);
break;
}
}
}
if(i==0)
{
[letters appendString:[a substringWithRange:NSMakeRange(0,i+1)]];
}
}
NSLog(@"%@",letters);
}

return 0;
}