思路：
1、创建两个栈
linkstack * operand ;//运算数栈
linkstack * operator;//运算符栈
2、扫描表达式。
<1>若是运算数,合并成一个完整的数data。
规则：直接入操作数栈
push_stack(operator_stack,data);(Ideas:
Create two stacks
Linkstack * operand;/ / operation number stack
Linkstack * operator;/ / operator stack
2. Scanning expression.
< 1 > is a complete number of data if the operands are counted.
Rule: go straight to the operand stack
Push_stack (operator_stack, data);)