C++ :: Add And Minus From Text File Not Give Right Value

I'm creating a bank system.

So I know to make a deposit to the balance, which add ups what is the balance to i have add.

When i run the deposit function, its work well in some ways. If balance(text file) has the value 10, add i addSum 20, the balance will become 30, same as the text file will become 30. so its work well to add positive number.

Code:
double deposit(double balance) {
double addSum = 0;
system("CLS");
cout<< "Welcome to deposit."<<endl;
cout<<"Enter a sum you wish to add to your account:";

[code]...

When I withdraw from 30 which is the balance, then i takeSum, for example i take away 30. The balance will become 30 - 30 = 0 When i make another withdraw from example -150, it will be -150.Which shows correct.

But when i make a deposit from -150 and i addSum 130, the balance shows -500, and it should had been -20.

Code:
double withdraw(double balance) {
double takeSum = 0;
system("CLS");
cout<< "Welcome to withdraw."<<endl;
cout<<"Enter a sum you wish to take away from your account:";

[code]...