由两个栈实现一个队列

#include<iostream>
#include<exception>
#include<stack>//使用栈
using namespace std;
template<typename T> class queue{//模板类的定义
public:
queue(void);
~queue(void);
void appendtail(const T& num);//成员函数一般是共有的
T deletehead();
private:
stack<T> stack1;//成员变量私有化
stack<T> stack2;
};
template<typename T> queue<T>::queue(void)//模板类函数的定义
{
}
template<typename T> queue<T>::~queue(void){
}
template<typename T> void queue<T>::appendtail(const T& num)
{
stack1.push(num);
}
template<typename T> T queue<T>::deletehead()
{
if (stack2.size()>0)
{
T head = stack2.top();
stack2.pop();
return head;
}
else if (stack2.size() <= 0)
{
if (stack1.size() > 0)
{
while (stack1.size() > 0)
{
T data = stack1.top();
stack1.pop();//栈的使用
stack2.push(data);
}
T head = stack2.top();
stack2.pop();
return head;
}
}
else
throw exception("empty!");
}
int main()
{
queue<char> qe;//由模板类定义对象
qe.appendtail('a');
qe.appendtail('b');
qe.appendtail('c');
qe.appendtail('d');
char head;
cout << (head = qe.deletehead()) << endl;
cout << (head = qe.deletehead()) << endl;
qe.appendtail('e');
cout << (head = qe.deletehead()) << endl;
cout << (head = qe.deletehead()) << endl;
cout << (head = qe.deletehead()) << endl;
}