在将nvarchar值转换成数据类型int时失败

<span style="font-size:14px;">    class Program
{
public int UserLogin(string name, string pwd)
{
try
{
string str =
string.Format(
"select count(*) from tb_user where <strong><span style="color:#ff0000;">u</span></strong><span style="color:#ff0000;"><strong>serName ={0} and userPassWord = {1}</strong></span>", name, pwd);

SqlCommand cmd = new SqlCommand(str, sql);

cmd.CommandType = CommandType.Text;

cmd.CommandText = str;

SqlDataAdapter da = new SqlDataAdapter(cmd);

da.SelectCommand.Connection.Open();

nCount = Convert.ToInt32(da.SelectCommand.ExecuteScalar());

da.SelectCommand.Connection.Close();

sql.Dispose();
}
catch (Exception e)
{
Console.WriteLine(e.Message.ToString());
}
return nCount;
}

static void Main(string[] args)
{
            Program aa = new Program();
            int nCount = aa.UserLogin("1","1");

            Console.WriteLine("nCount = " + nCount);
            Console.ReadKey();
}
}</span>

<span style="font-size:14px;"><img src="https://img-blog.csdn.net/20160810104132612" alt="" />
</span>

<span style="font-size:14px;">
</span>

<span style="font-size:18px;color:#ff0000;"><strong>将上面红色部分改成：userName ='{0}' and userPassWord ='{1}'。再来运行一下，问题解决了!</strong></span>