# Calculator-III

Challenging

The fundamental difference between a calculator and computer is that a computer can be programmed in a way that allows the program to take different branches according to intermediate results, while calculators are pre-designed with specific functions built in. The distinction is not clear-cut: some devices classed as programmable calculators have programming functions, sometimes with support for programming languages Find more on wikipedia page...

In this series of missions you are going to build an elementary calculator.

As an input, you get a sequence of keys pressed, and, as the result of that function, you should show what will be shown on the screen when the last key is pressed. Be attentive, it's not always the result of the expression. Actually, playing with the physical calculator or app will really helps you to catch edge cases.

Max digit space of 5 is added. It means that the maximum number you can enter is "99999".

Expected behavior:

• beginning zeros should be removed, only-zeros number - converted to single zero;
• among +- signs between numbers, the last one should be taken;
• "==" means repeating the last operation;
• "+=" or "-=" - adding/subtracting the number (or operations result) before the combination (doubling the number/subtracting itself);
• the calculator ignores digit you enter after 5th;
• "-" for numbers < 0 is NOT taking digit place;
• if the abs(result) is more than 99999 - "error" is shown as a result.

Input: String.

Output: String.

Examples:

```assert calculator("90000+10000=") == "error"
assert calculator("90000+10000-10000=") == "error"
assert calculator("90000+10000-10000") == "10000"
assert calculator("123456789") == "12345"
```

How itâ€™s used: Calculators are widely used. Understanding the principles of its input and output are interesting and useful.

Precondition: Allowed characters: digits (0-9), signs plus (+), minus (-) or equation (=) and their combinations (+=, +-, == etc.). The number may contain no more than 5 digits.

Settings
Code:
Other:
Invalid hot key. Each hot key should be unique and valid
Hot keys:
•  to Run Code: to Check Solution: to Stop:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

`pip3 install checkio_client`

`checkio --domain=py config --key=`

Sync solutions into your local folder

`checkio sync`

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

`checkio serv -d`

Alternatevly, you can install Chrome extension or FF addon

`checkio install-plugin`
`checkio install-plugin --ff`
`checkio install-plugin --chromium`

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

Pair Programming (Beta-version)

Welcome to Pair Programming! Engage in real-time collaboration on coding projects by starting a session and sharing the provided unique URL with friends or colleagues. This feature is perfect for joint project development, debugging, or learning new skills together. Simply click 'Start Session' to begin your collaborative coding journey!

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