利用栈来求解表达式求值问题。用的是算数优先法，设置了两个栈：OPTR,用来寄存运算符；OPND,用以寄存操作数或运算结果。-Usage of the expression evaluation stack to solve the problem. Count method using a priority, set up two stacks: OPTR, for storage operator　OPND, for the storage operand or operation result.