C#变量的生存周期问题

namespace c1
{
public class stack是
{
private int []arr;
private int sp; //栈顶
private int count;
public stack(int length)
{
count=length;
sp=0;
arr=new int[length];

}
public stack()
{
count=10;
sp=0;
arr=new int[10];

}
public void push(int element) //压栈
{
if(sp>=count)
MessageBox.Show("已超出栈顶，压栈失败","栈已满");
else
{
arr[sp]=element;

sp=sp+1;
}

}

public int pop() //出栈
{
if(sp<=0)
{
MessageBox.Show("栈为空,出栈失败");
return(0);
}
else
{
sp=sp-1;
return(arr[sp]);
}
}
}
}

Button1的Click事件代码