keypad interfacing using 8051

I am trying to write program for simple calculator. actually I wanted to understand interfacing of keypad with micro controller. so I decided to make small calculator I have keypad, 8051 and LCD. Previously I have been written C program for LCD Display. I am having problem to write code for keypad. This is hardware design
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I have been gone throw some tutorials and visited on some web sites but I am having difficulty to write program. can any one tell me what...

keypad interfacing using 8051