OC-nsstring可变与不可变增删改查代码块

NSString *str=@"fsdggfhjtyhdrfsdh";
       //单个删除
       NSString *str1=[str
substringFromIndex:1];
       NSLog(@"%@",str1);
       //选择删除
       NSString *str2=[str
substringWithRange:NSMakeRange(0,3)];
       NSLog(@"%@",str2);
       //添加
       NSString *str3=[str1
stringByAppendingString:str2];
       NSLog(@"%@",str3);
       //修改
       NSString *str4=[str
stringByReplacingOccurrencesOfString:@"sdgg"withString:@""];
       NSLog(@"%@",str4);
       NSMutableString *sr=[NSMutableStringstringWithFormat:@"%@",@"sdfdgdfg"];
       //增加
       [sr appendFormat:@"ad"];
       NSLog(@"%@",sr);
       //增加
       [sr append Format:@"%@",@"ad"];
        NSLog(@"%@",sr);
       //删除
       [sr deleteCharactersInRange:NSMakeRange(0,3)];
       NSLog(@"%@",sr);
       //插入
       [sr insertString:@"ddddd"atIndex:4];
       NSLog(@"%@",sr);
       //修改
       [sr replaceCharactersInRange:NSMakeRange(0,4)withString:@""];
        NSLog(@"%@",sr);