A gridview that consist of two columns named as Present and pres [duplicate]

The problem is I have a lot of rows in gridview but when I checked a certain or any Checkbox, I wasn't able to add 1 in present column.

I just try that whenever I click a any Checkbox under column name "pres" it Will add 1 in "Present" column that is used for counting number of time when checkbox checked... I just need a code that whenever in any row of gridview under "pres" column I check a specific checkbox it will automatically add 1 to corresponding "Present" column value