Apologies if this is a duplicate. I have a helper function called inputString() that takes user input and returns a String. I want to proceed based on whether an upper or lowercase character was entered. Here is my code: 

```
 print("What do you want to do today? Enter 'D' for Deposit or 'W' for Withdrawl.")

    operation = inputString()

    if  operation == "D" || operation == "d" {

        print("Enter the amount to deposit.")

```

My program quits after the first print function, but gives no compiler errors. I don't know what I'm doing wrong.