c# – 错误：索引超出数组的边界.

我有一个int数组是0 – 8,这意味着它可以容纳9个int,正确吗？
我有一个int被检查,以确保用户的输入值为1-9.我从整数中删除一个(像这样)

if (posStatus[intUsersInput-1] == 0) //if pos is empty
{
    posStatus[intUsersInput-1] += 1; 
}//set it to 1

然后我自己输入9,我得到错误.它应该访问数组中的最后一个int,所以我不明白为什么我得到一个错误.
相关代码：

public int[] posStatus;       

public UsersInput()    
{    
    this.posStatus = new int[8];    
}

int intUsersInput = 0; //this gets try parsed + validated that it's 1-9    

if (posStatus[intUsersInput-1] == 0) //if i input 9 it should go to 8?    
{    
    posStatus[intUsersInput-1] += 1; //set it to 1    
}

错误：

"Index was outside the bounds of the array." "Index was outside the bounds of the array."