从文本框获取上限和下限

I'm trying to figure out the code for a project but I don't completely understand it. The objective is to write a program that generates a set of 10 random numbers and stores it in an array (the 10 numbers display in the textbox correctly). It should have a button that will compute the minimum, maximum and average of the array. I cant seem to get the max and min values of it from a textbox. I know people don't post the answers and I'm not looking for that but if someone could tell my why what I'm doing for the max/min is wrong or point my in the right direction I would appreciate it. Thank you!I'm trying to figure out the code for a project