函数中的集合和  数学中的集合 基本上差不多 集合中每个元素最多只能出现一次  并且 当元素储存到set集合之中 会自动 按照 ascll 进行  从小到大的  排序

大神关于   set   的 详细总结    http://www.cnblogs.com/BeyondAnyTime/archive/2012/08/13/2636375.html

Andy, , has a dream - he wants to produce his
very own dictionary. This is not an easy task for
him, as the number of words that he knows is,
well, not quite enough. Instead of thinking up all
the words himself, he has a briliant idea. From
his bookshelf he would pick one of his favourite
story books, from which he would copy out all
the distinct words. By arranging the words in
alphabetical order, he is done! Of course, it is
a really time-consuming job, and this is where a
computer program is helpful.
You are asked to write a program that lists
all the different words in the input text. In this
problem, a word is defined as a consecutive sequence
of alphabets, in upper and/or lower case.
Words with only one letter are also to be considered. Furthermore, your program must be CaSe InSeNsItIvE.
For example, words like “Apple”, “apple” or “APPLE” must be considered the same.
Input
The input file is a text with no more than lines. An input line has at most characters. Input
is terminated by EOF.
Output
Your output should give a list of different words that appears in the input text, one in a line. The
words should all be in lower case, sorted in alphabetical order. You can be sure that he number of
distinct words in the text does not exceed .
Sample Input
Adventures in Disneyland
Two blondes were going to Disneyland when they came to a fork in the
road. The sign read: "Disneyland Left."
So they went home.
Sample Output
a
adventures
blondes
came
disneyland
fork
going
home
in
left
read
road
sign
so
the
they
to
two
went
were
when

#include
#include
#include
#include
using namespace std;
setdict; // 定义一个 set 集合
int main()
{
string s,buf;
while(cin>>s)
{
for(int i=;i>buf)
dict.insert(buf); /*这一种对文本处理的 方式 很好*/
}
for(set::iterator it=dict.begin();it!=dict.end();++it)
cout<<*it<<endl;
return ;
}