// plural(n,s)
//
// 用法：为字符串加s变为复数，当n的取值不是+/-1时，就在s后添加后缀"s";当n的取值是+/-1时，就在s后不加后缀"s"
//n为1,不加s
. disp plural(1,"banana")
banana
//n为2,加s
. disp plural(2,"banana")
bananas
//n为2,加s
. disp plural(2,"horse")
horses
//n为-1,不加s
. disp plural(-1,"horse")
horse
//n为0,不是1或-1,加s
. disp plural(0,"horse")
horses
//n为0,不是1或-1,加s
. disp plural(0,"horsx")
horsxs
.
// plural(n,s1,s2)
//用法：
// 可以给s1添加删减后缀。当n的取值不为+/-1时，以s2指定的形式修正("+"或"-")或替代。
//如果s2前有"+"，表示将s2加到s1后；如果s2前为"-"，则返回s1中去掉s2 字符串后剩下的字符串；如果s2前既没有"+"也没有"-",则plural(n,s1,s2)=s2。
//n为2,+s2,连接hot+pot=hotpot
. disp plural(2,"hot","+pot")
hotpot
////n为2,-s2,连接bookpot-pot=book
. disp plural(2,"bookpot","-pot")
book
////n为2,s2,结果为s2)
. disp plural(2,"book","pot")
pot
//n为1，结果为s1
. disp plural(1,"hot","+pot")
hot
//n为1，结果为s1
. disp plural(1,"bookpot","-pot")
bookpot
//n为1，结果为s1
. disp plural(1,"book","pot")
book
