Why is the null coalescing operator breaking my string assignment in c#?

Question

I'm creating a query string in a web form, and I'm dealing with values from the parameters that might be null. There are lots of ways to check and fix these, but the most elegant one I found is the following:

string pass;
pass = "BillabilityDetail.aspx?_startDate=" + _startDate.Text + "&_endDate=" + _endDate.Text + 
       "&_isContractor=" + _isContractor.SelectedValue + "&_busUnit=" + _busUnit.Text 
       + "&_projectUnit=" + _projectUnit.SelectedValue + "&_leadCon=" + _leadCon.Value ?? -1
       + "&_acctExec=" + _acctExec.Value ?? -1 + "&_isBillable=" + _isBillable.SelectedValue + 
       "&_isActive=" + _isActive.SelectedValue + "&_include=" + _include.SelectedValue;

The only issue is... it doesn't work. When the code reaches this part,

"&_leadCon=" + _leadCon.Value ?? -1 + "&_acctExec=" + _acctExec.Value ?? -1 

the string stops assigning values. So the string would end with &_leadCon=. I know of ways to work around this, but I don't know why it stopped working in the first place. Any tips?

Answer 1

The + has higher precedence than ??, thus you need to surround your null-coalescing expressions in parenthesis.

"&_leadCon=" + (_leadCon.Value ?? -1) + "&_acctExec=" + (_acctExec.Value ?? -1 )

See the precedence chart here

Answer 2

Try using parentheses to tell the compiler exactly what you mean.

For example:

"&_leadCon=" + (_leadCon.Value ?? -1) + "&_acctExec=" + (_acctExec.Value ?? -1)