创建了一个界面，可以选择txt文件，并统计其中的各种字符出现次数。-Create an interface, you can choose txt file, and statistics on the number of occurrences of various characters.

MFC界面统计字符频率:输入一个字符串，统计里面的字母的频率，输出不是字母的字符。-Calculate rates of characters under MFC