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.