I want you to write a code in C$,$ not C$++,$ for customer communications invoices by using functions. The functions are a function to enter the user name, a function to enter the phone number, a function to enter the amount paid, a function for the amount of balance and the number of minutes, as well as a function to search for a user from the customers who have been entered, a function to display customer lists, and a function to move between functions.