//文件名:CHAPTER7-21.cpp
#include <iostream>
#include <deque>
#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
#endif 
typedef deque<char >  CHARDEQUE;
void print_contents (CHARDEQUE  deque, char*);
int main()
{   //create an empty deque a
    CHARDEQUE  a;
    //check whether it is empty
    if(a.empty())  cout<<"a is empty"<<endl;
    else  cout<<"a is not empty"<<endl;
    //inset A, B, C and D to a
    a.push_back('A');
    a.push_back('B');
    a.push_back('C');
    a.push_back('D');
    //check again whether a is empty
    if(a.empty()) cout<<"a is empty"<<endl;
    else cout<<"a is not empty"<<endl;
    //print out the contents
    print_contents (a,"a");
    cout <<"The first element of a is " <<a[0] <<endl;
    cout <<"The first element of a is " <<a.at(0) <<endl;
    cout <<"The last element of a is " <<a[a.size()-1] <<endl;
    cout <<"The last element of a is " <<a.at(a.size()-1) <<endl;
}
//function to print the contents of deque
void print_contents (CHARDEQUE  deque, char *name)
{   CHARDEQUE::iterator pdeque;
    cout <<"The contents of "<< name <<" :";
    for(pdeque = deque.begin(); pdeque != deque.end(); pdeque++)
    {  cout <<" "  << *pdeque; }
    cout<<endl;
}