How to set a value to Unbound Column cell ? (SetRowCellValue)

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C#

WinForms

Gridview

DevExpress

I can able to set value to Bounded Column.
I used this code

int c = a + b;
gridView1.SetRowCellValue(gridView1.FocusedRowHandle, gridView1.Columns["boundcolumn"], c);

But I want to Set the this c value to Unbound Column. this code not working to Unbound Column. How to set value to Unbound Coulmn ?