//2.10实现一个秒表功能(精确到0.01秒)，有计时按钮和复位按钮，

//当安下计时按钮时开始计时，同时计时按钮文字由“开始计时”变为“停止计时”，

//再次按下计时按钮停止计时同时显示文字变为“开始计时”，按下复位按钮后时间回到0:-//2.10 implement a stopwatch function (accurate to 0.01 seconds), with timing button and reset button,// when the safety button, the next time start time, while timing the button text from " start time"　to " stop the clock" ,// Press the timer button again to stop time while the display text to " start time" , press the reset button and time back to 0:00