I think my code is correct but still my simulation software is behaving abnormally.

check my code at

http://pastebin.com/JiQ5RTEX



this forum doesn't let me attach the proteus design file so i am giving the screen shot. pressing key in the keypad don't do anything and the numbers 1, 4, 7 and 0 shows up on the seven segment with some delay. Seems like the simulation software is not recognizing the "if" statement.

 

I do not use simulation software to debug code.
Why not debug the actual code on a real system?

 

Because the real system costs a lot. I don't have money to buy components and burner right now. And it also takes a lot of time and give a lot more frustration when we fail.