Get No. Of Days From TextBox

Question

in my databasae table i have to coloumn

 

one coloumn for issueDate and one for leaveDate

i get issueDate and LeaveDate from database and show them in textbox

But the problem is 

i want to get on no of days

 for example

 

issue date =12/12/2014

leave date=12/10/2012

 

reamin=12-10=2

 

i want this  kindly tell me how i can get only only days from textbox and calculate there difference??????????