 　　数学表达式词法分析及实现

要求能将用户输入的任意数学表达式语句正确理解，并编程实现表达式运算结果的正确输出，用户界面可以是基于字符型的Dos界面或图形界面-　lexical analysis and realization of the mathematical expression required the user can enter any mathematical expression statements correct understanding and programming the expression computing the correct output results, the user interface is based on the character of the Dos interface or graphical interface