PIC16F877A using CCS

HI i got a project but did not really know about the program...
1)i want PIC use a keypad that can use keypad as calculator with 2 digit
example=20+10=30
Is there anyone can help me or know the code...
1)i want PIC use a keypad that can use keypad as calculator with 2 digit
example=20+10=30
Is there anyone can help me or know the code...