How to write program

I am trying to write keypad program, I work with 8051 and keil compiler so I did google search and I found so many links . I have read following three links but still I am confuse because the program has been written differently in all the three links and I don't understand how to write proficient program for keypad interfacing.

https://electrosome.com/interfacing-keypad-8051-microcontroller-keil-c/...

How to write program