Hi everyone, I'm new to the 8051 world and I am working on a calculator project with a PJRC board, a 4x4 keypad, and an LCD. I have gone through the tutorials on arithmetic from this site, and the subroutines have helped me alot. The problem I'm having is in deciding how to work my program flow.

My original idea was pretty normal:
1)Get 1st input from user
2)Get operand(+,-,x,/) 3)Get 2nd input from user 4)Get = sign from user for result.

I also thought I could work it this way:
1)Get 1st and 2nd inputs from user 2) Get operand 3)Get result.

I guess the problem I am having is how this works into the subroutines. When I get the inputs from the user, I need to first convert the number to hex and then save to hex, and when and where I should move the inputs into the registers(in the main code or in the actual subroutines). I am also unsure as how to interface my keypad to the board so that certain inputs correspond to their respective routines. My email is eco7@hotmail.com. Thanks guys.