The Edison has the command configure_edison --wifi which configures the Wi-Fi connection. If you don’t want to enter in the Edison's terminal to run the command, I would suggest you to modify the code of the Python script configure_edison.py to request the inputs from the keypad and to display the outputs in the LCD. The only detail is that you have to use Python and not C, because the configure_edison.py is a Python script.
The configure_edison.py script is accessible in the following file: /usr/bin/configure_edison. You can make a copy of it (or just a copy of the part that you need), and modify it by adding the code to request data from the keypad and to display data in the LCD.
That was prompt. Will try to modify the file and run.