字符串匹配，使用有限状态自动机原理实现，并解释转义字符 \\ -String matching, the use of finite state automata theory to achieve, and explain the escape character ' \ \'

在Fedora Linux下编写的C语言程序。可以将文本文件中的表达式构造成语法树并计算求值。表达式如存在语法错误，表达式语法错误可由相关自动机发现。代码适合：学习自动机和语法树的初学者。-C codes under Fedora Linux. The codes can transform expressions in text file to a parse tree. Grammar mistakes could be detected by a finite automata. This