一元多项式的加减的实现。本程序的特色是

不会因为要接收数字而用户输入的是字母时发生死循环。

输入的项会自动合并同类项和自动按从高次到低次排列。-One dollar to achieve the addition and subtraction of polynomials. Characteristics of this procedure is not necessary to receive digital and letters entered by the user when the cycle of death. The item will automatically enter the merger of similar items and automatically from high-to low-order.