说明：  通过模拟一个简单的计算器来进行+、-、*、/、%、^（乘方）等运算，从键盘上输入一算术表达式（一般为中缀表达式），计算出表达式的值。
(By simulating a simple calculator for +, -, *, /,%, ^ (multiplier) and other operations, an arithmetic expression (usually infix expression) is input from the keyboard to calculate the value of the expression.)