想创建一个动态栈，但是修改的时候出了一个问题

#include
using namespace std;
class seqstack
{
private:
int top;//顶指针
int* data;//建立数组
public:
seqstack()
{
int size;
cin >> size;
int* data = new int[size];
top = -1;
}

void output()
{
    cout << endl;
    cout << "当前栈的长度为：" << top + 1 << endl;
    if (top != -1)
    {
        for (int i = 0; i <= top; i++)
        {
            cout << "当前栈的内容为：" << data[i] << endl;
        }
    }
}

void insert(int value)
{
    top++;
    data[top] = value;
}

int pop()
{
    int temp = data[top];
    top--;
    return temp;
}

void getlength()
{
    cout << "长度为：" << top + 1 << endl;
}

};
int main()
{
seqstack mystack;
cout << endl;
mystack.output();
for (int i = 0; i < 10; i++)
{
mystack.insert(i);
}
return 0;
}

这个就算分配了50的空间，也会运行中止，哪里错了呢？

http://www.cnblogs.com/scrat/archive/2012/08/22/2650812.html