个字符串常见算法系统总共包括12个模块。每个模块都是并列的，分别对应相应的字符串算法。只要输入相应的数字就能进入此模块然后进行相应的操作。而输入可以随意输入一个字符串（可以包含空格）.我的第一个模块是求字符串的复制；第二个模块是字符串的比较；第三个模块是求字符串的长度 ；第四个模块是连接两个字符串；第五个模块将ch字符转换为小写母 ；是第六个模块是；将ch字符转换为大写字母 ；第七个模块是检查ch是否是字母；-Common algorithm string system includes 12 modules in total. Each module is parallel, corresponding to the corresponding string algorithm. Just enter the corresponding number will be able to access this module and then the appropriate action. The input can be free to enter a string (can contain spaces). My first module is seeking a copy of the string　second module is a string comparison　third module is the pursuit of the string length　fourth string connecting the two modules　fifth module will be converted to lowercase characters ch mother　is the sixth module　the character ch converted to upper case letters　seventh module is to check whether ch is a letter