Keep user data even after the program is exited

So I'm trying to create a simple banking program just to test my skills, but I was wondering how do I make it so that the user's data is kept. My plan is to create a .h file that handles all the balance, deposit, and withdraw stuff. But as far as I know once the user exits the program, it will delete the data and it will be gone. How do I make it so that the data stays no matter what. So like in this session the user has a balance of $1000 and makes a withdrawal of $100. Then exits. Next time they open the program that balance should be $900. How do I make that happen. BTW doing this all in c++