4 Bits magnitude Comparator

Hi, 

I want to make a 4 Bits magnitude comparator. its my final project of DLD.

SPECIFICATION ARE:

its input must be by keypad and then input will be displayed on 7 segment dispaly and then the comparing begins.

My question is that how can i convert the keypad input into BCD to transfer it into my comparator combinational circuit and tell me if there is need of any register to store my inputs.

kindly help.