$1.$ Main menu: Create a main user menu to display the main options to the user. User have the

option to choose between $1$ and $4.$ The program will display an error message if user option is

not within the valid selection $($less than $1$ and greater than $4).$ Think about using a conditional

structure to serve the user choice. Invalid option $($for e$.$g$.6)$ can be handled with default else

block $($please see sample I$/$O for error message$).$ A main menu is as follows and detailed of each

option is provided below:

$1.$ Order Laptop

$2.$ Order Cell Phone

$3.$ Checkout

$4.$ Quit