说明：  逆波兰式定义: 将运算对象写在前面，而把运算符号写在后面。用这种表示法表示的表达式也称做后缀式。逆波兰式的特点在于运算对象顺序不变，运算符号位置反映运算顺序。采用逆波兰式可以很好的表示简单算术表达式，其优点在于易于计算机处理表达式。
(Reverse Polish definition: The object EDITORIAL computing, and the operator symbols written on the back. Use this expression, said expression is also known as the suffix type. Reverse Polish-style features of the order of operands is the same, the location of computing symbols reflect the order in computing. The use of Reverse Polish-style can be very good that a simple arithmetic expression, and its advantage is easy to computer processing expressions.)