The calculator

The first calculator was invented in 1966 at Texas Instruments (http://www.ti.com/corp/docs/company/history/timeline/eps/1960/docs/67-handheld_calc_invented.htm) and was able to do addition, subtraction, multiplication, and division. The calculator had eighteen keys and could display twelve numbers on the screen. While it doesn't seem like much at first, especially compared to the technology we now enjoy, there is quite a lot of code and decision making that go into the operations that a basic calculator performs.

When we want to figure out how something works, we need to break it down into smaller parts. Let's take a look at how the calculator adds numbers together:

1. First, the calculator needs power.
2. The user enters the first number.
3. The user presses an operation key (+, -, *, or /).
4. The user enters a second number.
5. The user presses the = key.
6. Then, an answer is printed to the screen.

On a basic calculator, the computer does not keep all of the numbers on the screen....