NSMutalbleDictionary

      //创建一个空的可变字典
        NSMutableDictionary *dicM = [NSMutableDictionary dictionary];
        //给可变字典赋值
        [dicM setObject:@"lxc"forKey:@"name"];
        //取出键值对添加到dicM中
        [dicM setValuesForKeysWithDictionary:@{@"age":@"23",
                                               @"height":@"1.78"}];
        
        //获取字典中key对应的值
        NSString *name = dicM[@"name"];
        //删除字典中的key和对应的值
        [dicM removeObjectForKey:@"height"];
        //修改字典中key对应的值
        [dicM setObject:@"18" forKey:@"age"];
        //如果在不可变字典出现了同名的key，那么后面的key对应的值不会保存
        NSDictionary *dic = @{@"name":@"cyf",@"name":@"xxx"};
        //如果在可变字典出现了同名的key，那么后面的key会覆盖前面的
        NSMutableDictionary *dM = [NSMutableDictionary dictionaryWithObjects:@[@"lxc",@"cyf"] forKeys:@[@"name",@"name"]];
        //NSArray是有序的，NSDictionary是无序的
        //NSArray是通过脚标的方式访问元素，NSDictionary是通过key访问元