C＃SQL插入。 使用未分配的局部变量？

Question

My application is saying totalTokens is use of an unnassigned local variable and I am not seeing why. I must be missing something obvious. Here is the line. Full code is below. Thanks

    myCommand.Parameters.Add("@Tokens", totalTokens);



    private void btnSave_Click(object sender, EventArgs e)
    {
        string date = dateTimePicker1.Value.ToShortDateString();
        bool library = chkLibrary.Checked = true;
        string libReason = txtReason.Text;
        int libMin = Int32.Parse(txtLibTime.Text);
        int hwMin = Int32.Parse(txtHwTime.Text);

        int partialTokens;
        int totalTokens;
        int totalHw;

        // calculate Total homework
        totalHw = libMin + hwMin; 

        // calculate bonus library time
        partialTokens = totalHw / 15;

        // calculate Total tokens
        if (chkLibrary.Checked == true)
        {
            totalTokens = partialTokens + 1;
        }

        using (SqlCeConnection con = new SqlCeConnection(conString))
        {
            SqlCeCommand myCommand = new SqlCeCommand("INSERT INTO ChangeTable" + 
            "(Date, Library, LibMissed, LibTime, HwTime, TotalHomework, Tokens)" +
            "VALUES(@Date, @Library, @LibMissed, @LibTime, @HwTime, @TotalHomework, @Tokens)", con);

            myCommand.Parameters.Add("@Date", date);
            myCommand.Parameters.Add("@Library", library);
            myCommand.Parameters.Add("@LibMissed", libReason);
            myCommand.Parameters.Add("@LibTime", libMin);
            myCommand.Parameters.Add("@HwTime", hwMin);
            myCommand.Parameters.Add("@TotalHomework", totalHw);
            myCommand.Parameters.Add("@TotalHomework", totalTokens);

            con.Open();
            myCommand.ExecuteNonQuery();
            con.Close();

            RefreshGrid();
        }
    }

Answer 1

The totalTokens variable is only assigned a value if the condition in the if statement is true. You have to make sure that the variable always has a value.

Perhaps you meant something like:

// calculate Total tokens
if (chkLibrary.Checked == true)
{
  totalTokens = partialTokens + 1;
} else {
  totalTokens = partialTokens;
}

Side note: When you use the variable, you are assigning two values to the same parameter, which will of course overwrite the first value:

myCommand.Parameters.Add("@TotalHomework", totalHw);
myCommand.Parameters.Add("@TotalHomework", totalTokens);

Judging from the parameters used in the query, it should be:

myCommand.Parameters.Add("@TotalHomework", totalHw);
myCommand.Parameters.Add("@Tokens", totalTokens);

Answer 2

totalsTokens will only be assigned if chkLibrary.Checked is true . If it is false then it would remain unassigned.

Answer 3

 if (chkLibrary.Checked == true)
        {
            totalTokens = partialTokens + 1;
        }

this is the only time totalTokens is assigned to..... so if chkLibrary.Checked isn't checked, then it's an unassigned variable.

Not sure what you want it to be by default? but perhaps when you declare it you want

int totalTokens = 0;

Answer 4

Wheres this line on your code

myCommand.Parameters.Add("@Tokens", totalTokens);

you should have this between myCommand initialization and con.Open();

Answer 5

totalTokens is only initialized inside that conditional; thus it's not guaranteed to be set when you call myCommand.Parameters.Add("@TotalHomework", totalTokens); .

Just initialize it to something (like 0) where you declare it, and the warning should go away.

Answer 6

The fix is basically assign it SOME kind of value when you create it, for example

int partialTokens = 0;
int totalTokens= 0;
int totalHw = 0;

Currently, it is possible it will be used without having a value assigned, due to the assignment inside a conditional statement.