C# 保存上次输入的值

参考链接：
https://bbs.csdn.net/topics/390247378
https://social.msdn.microsoft.com/Forums/zh-CN/ca377a00-851d-4703-8105-383d35ff9e48/2085120110c?forum=visualcshartzhchs
https://www.cnblogs.com/maijin/p/6738340.html
https://www.cnblogs.com/Embrace-solitude/p/13453083.html
https://www.cnblogs.com/zhangzhu/articles/2828058.html
https://blog.csdn.net/qq_43026206/article/details/105723808
https://blog.csdn.net/cysong168/article/details/6161276