错误显示如下输入字符串格式不正确

问题描述

我正在验证用户是否输入了textbox1，学生ID是否在数据库中。



该代码如下;

i am validating whether the user enters in the textbox1 student id is there in the database or not.

for that code as follows;

SCon.Con.Open();
       string str = "Select  count(*)  from Studdet where studid = '" + txt_Studid.Text.ToString() + "'";
       SqlCommand cmd = new SqlCommand(str, SCon.Con);
       int a = Convert.ToInt16(str);
       int count = (int)cmd.ExecuteScalar();
       if (count > 0)
       {
           Label4.Text = "Correct Student id";
           return;
       }
       else
       {
           Label4.Text = "InCorrect student id is there";
           return;
       }
          SCon.Con.Close();

在运行模式下，当我在textbox1中输入学生ID并单击按钮时显示如下错误;



输入字符串格式不正确





什么是我上面的代码中的问题请帮帮我。



问候，

Narasiman P.

in the run mode when i enters the student id in the textbox1 and click the button shows error as follows;

input string was not in a correct format


what is the problem in my above code please help me.

Regards,
Narasiman P.

推荐答案

SCon.Con.Open();
        string str = "Select  count(*)  from Studdet where studid = " + txt_Studid.Text.ToString() ;
        SqlCommand cmd = new SqlCommand(str, SCon.Con);
        int a = Convert.ToInt16(str);
        int count = (int)cmd.ExecuteScalar();
        if (count > 0)
        {
            Label4.Text = "Correct Student id";
            return;
        }
        else
        {
            Label4.Text = "InCorrect student id is there";
            return;
        }
               SCon.Con.Close();

int a = Convert.ToInt16(str);

因为str有

because str have "

Select count(*) from Studdet where studid

永远不会转换为int

请删除此行并执行此操作你收到的结果

..

"
which is never convert to int
please remove this line and execute this you get result
..

SCon.Con.Open();
string str = "Select count(*) from Studdet where studid = '" + txt_Studid.Text.ToString() + "'";
SqlCommand cmd = new SqlCommand(str, SCon.Con);
int a = Convert.ToInt16(str);
int count = (int)cmd.ExecuteScalar();
SCon.Con.Close();
if (count > 0)
{
Label4.Text = "Correct Student id";
return;
}
else
{
Label4.Text = "InCorrect student id is there";
return;
}
</pre>



thanks

and also closed connection before return because it will un-reachable code.
if problem persist please give me your reviews.,...

int i = String.IsNullOrEmpty(str) ? -1 : Convert.ToInt16(str);

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