How to re-direct functions?

[AmateurPCGuy]

Be Forewarned: You're dealing with someone with very little experience with C++ programming.

 

Hi.

Basically, I'm putting together an ATM program as part of our subject. I got most of the core ATM stuff (Balance Inquiry, Withdraw, Deposit) except the Change PIN feature.

Here's the outline for better understanding: 

I got around up till the Change My Pin part, after that, I got nothing since I get to lots of problems if I make a new PIN entry code that's re-directing to the Main menu if completed. That certain error is "redefining functions" error where it just says that all functions on the program (basically, the whole program) is already defined somewhere else.

The question is: How am I gonna proceed after I changed my PIN code? 

[vorticalbox]

how is the pin stored currently?

[as96]

We need the code to fix that kind of error.