How do I create a simple electronic calculator being able of performing simple addition and subtraction?

Question

Its our project so it can be as simple as possible. but we were just having a problem with letting the calculator decide to display the difference if the subtraction sign was pressed and the sum if the addition sign was pressed. Please help us

Schematic Diagrams can Help

actually we've started on it
were using a 4008 for adding the bits.
we've also used a complementor that is to make the bits in their 2's complement for subtracting.

an i forgot it was just a 1 digit calculator

Answer 1

Start with a full adder, and gang together as many as you need.

Answer 2

There is no practical way to do this on a realistic scale without using a commercial calculator chip -- a breadboard circuit capable of recognizing and adding or subtracting even one digit would involve a minimum of eight flip-flops and a fistful of gates, not to mention display drivers. If you use a commercial chip, the chip architects will have defined all of the gritty detals of exactly what each button press does. If you want to do a one-digit add/subtract and deide that the hardware list I have cited is manageable, then you just have to design the circuit and wire it up. Doable, but not trivial.

Answer 3

Must established some assumptions as the criterion of the correctness of the analogue indicate how to extend the language in this way ,with clarify in a specific languages or programming

Answer 4

Abacus!