Question

c++类的动态数组怎么建立？

以下是我写的实现栈的代码，我想让stack类中的entry数组实现动态，即，我输入一个值，使他等于maxstack，这样来定义entry数组的大小。而不是现在的，给maxstack赋予100；请问怎么才能够实现，谢谢！！
#include <iostream>
using namespace std;
int count=0;
const int maxstack=100;
class stack

{
private:

char item;
char entry[maxstack];
public:

void clear();
void pop();
char top(char item);
void push(char item);
bool empty();

};

void stack ::push( char item)
{
if(count>=maxstack)
{
cout<<"overflow";
}
else
{
entry[count++]=item;
}

}
char stack ::top(char item)
{
if (count==0)
{
cout<<"underflow";
}
else
{
item=entry[count-1];
}
return item;

}
void stack ::pop()
{
if(count==0)
{
cout<<"underflow";
}
else
{
count--;
}
}

bool stack :: empty()
{
if(count==0)
{
return true;
}
else
{
return false;
}
}
void stack ::clear()
{
count=0;
}
int main ()
{
char ch;
stack cha;

cout<<"please enter a single line of text"<<endl;
cout<<"then it will write out the characters in the line in reverse order !"<<endl;

while((ch=cin.get())!='\n')
{
cha.push(ch);
}
while(!cha.empty())
{
ch = cha.top(ch);
cha.pop();
cout<<ch;

}
cout<<endl;
return 0;
}

Answer 1

修改如下：
//---------------------------------------------------------------------------

#include <iostream>
using namespace std;
int count=0;
//注意这里
class stack

{
private:

char item;
char *entry;//注意这里
int maxstack ; //注意这里
public:

stack(void);//注意这里
void clear();
void pop();
char top(char item);
void push(char item);
bool empty();
~stack(); //注意这里

};

stack::stack(void) //注意这里
{

cout<<"Maxstack=";
cin>>maxstack;
entry=new char[maxstack];
cin.ignore(255,'\n') ;
}
stack::~stack() //注意这里
{
delete []entry;
}
void stack ::push( char item)
{
if(count>=maxstack)
{
cout<<"overflow";
}
else
{
entry[count++]=item;
}

}
char stack ::top(char item)
{
if (count==0)
{
cout<<"underflow";
}
else
{
item=entry[count-1];
}
return item;

}
void stack ::pop()
{
if(count==0)
{
cout<<"underflow";
}
else
{
count--;
}
}

bool stack :: empty()
{
if(count==0)
{
return true;
}
else
{
return false;
}
}
void stack ::clear()
{
count=0;
}
int main ()
{
char ch;
stack cha;

cout<<"please enter a single line of text"<<endl;
cout<<"then it will write out the characters in the line in reverse order !"<<endl;

while((ch=cin.get())!='\n')
{
cha.push(ch);
}
while(!cha.empty())
{
ch = cha.top(ch);
cha.pop();
cout<<ch;

}
cout<<endl;
return 0;
}

//---------------------------------------------------------------------------

Answer 2

int maxstack=0;
cin>>maxstack;
char *p=new char[maxstack];