可输出中序遍历序列检测程序功能是否正确。如果每个分支节点用一个临时变量标记，则对四则运算表达式的抽象语法树进行后序遍历，可以得到输入表达式所对应的四元式序列（实验4要用到这样的四元式序列）-Preorder output sequence detection program functions correctly. If each branch node labeled with a temporary variable, then the abstract syntax tree arithmetic expressions were preorder, you can get input expression quaternion corresponding sequence (Experiment 4 to use this sequence quaternion )