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C# convert int to Null

I have a few drop down boxes which feed into a SQL query. The query is written so that any of the parameters can be Null and thus excluded from the query. If the selected value of any of the drop down boxes is 0 then i would like to set that parameter to null but I am getting compile time errors.
When I do Convert.ToInt32(null), it still returns 0.

pseudocode: if tddnRegionId.SelectedValue == 0 then make RegionID = null

Code below,
Thanks

protected void btnGo_Click(Object sender, EventArgs e)
    {
        int RegionIDNull = Convert.ToInt32(null);
        int RegionID; 

        RegionID = Convert.ToInt32(tddnRegion.SelectedValue) == 0 ? RegionIDNull : Convert.ToInt32(tddnRegion.SelectedValue);
            
        int Month = Convert.ToInt32(tddnMonth.SelectedValue);

        ResultsManager rm = new ResultsManager();
        try
        {
            DataSet ds = new DataSet();
            ds = rm.getEventDetailsForCalendar(RegionID, Month);

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ASKER CERTIFIED SOLUTION

gyoreg

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Guy Hengel [angelIII / a3]

what about:

 RegionID = Convert.ToInt32(tddnRegion.SelectedValue) == 0 ? null : Convert.ToInt32(tddnRegion.SelectedValue);

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AndyAinscow

The integer value of null is 0 (zero). So your code <int RegionIDNull = Convert.ToInt32(null)> is doing what you programmed it to do.

gyoreg

angelIII: You're right, but you cannot assign null value to a value type, except if it is nullable, as I mentioned above.

Stanton_Roux

ASKER

Thanks all,

This is what I did to make it work

protected void btnGo_Click(Object sender, EventArgs e)
{
int? RegionID = null;

RegionID = Convert.ToInt32(tddnRegion.SelectedValue) == 0 ? RegionID : Convert.ToInt32(tddnRegion.SelectedValue);
.
.
.