Istanbul is a hub for different nationalities. Either visiting Istanbul or working, most non Turkish citizens will need to exchange some money. This is not a problem.
All main streets in Istanbul offer great quantity of exchange offices with good rates, and also the normal banks also give you a pretty much faire price for your euros, dollars, dirhams or rials.
Most cash machines ATM accept international card so another option to skip exchanging money is to get money out with your bank car. Take in consideration that usually most banks add a tax for international money withdraw operations.