运行app，进入断点模式后，在（lldb）后输入
expr username = @"username"
expr password = @"badpassword"
控制台会返回以下信息
(NSString *) $0 = 0x3d3504c4 @"username"
(NSString *) $1 = 0x1d18ef60 @"badpassword"
现在跳出断点，执行断点之后的两条输出语句，控制台会有以下输出
(0x1c59aae0) A line for the breakpoint
(0x1c59aae0) Username and Password after: username:badpassword