构建vi，每秒显示0~1之间的随机数。与此同时，计算并显示最后产生的4个随机数的平均值。只有4个数后才显示平均值，否则显。(Building VI, displaying random numbers between 0~1 per second. At the same time, calculate and display the average value of the 4 random numbers at the end. Only 4 numbers are displayed before the average value is displayed otherwise.)