====== HW 02 - Calculator ======
The task is to write a simple program that performs the following basic integer arithmetic operations: addition, subtraction, multiplication and division.

You will get the operands from the standard input of your program as follows
<code>
<number of digits of the 1st operand>
<1st operand>
<operator +, -, *, />
<number of digits of the 2nd operand>
<2nd operand>
</code>

The operands can also be negative numbers starting with ''-'' (minus sign).

**The operands can also have more than 30 digits but less than 100 digits.** Thus, more than built-in types.

Your program is expected to print the result of the desired arithmetic operation on the standard output, and the return value shall be //0//. In the case of a division operation, round the result to the closest integer.

However, there might be situations when an unsupported operation (meaning not one of the listed above) is entered.
In such situations, the program prints //Error: wrong operator// and returns //2//.
Also, any of the operands on the input might contain non-digit symbols, and those situations should result in printing //Error: wrong operands// and returning //3//.
In any other erroneous situation, print //Error: unknown error// and return //1//.

You can check your solution using Python, [[https://www.wolframalpha.com/|WolframAlpha]] or any other tool. No external library is allowed.

<note tip>
fgets() function allows flexible reading of stdin

getchar() reads a single character from stdin

You can find other possibly useful functions in [[https://en.cppreference.com/w/c/io|stdio.h]] library

Recall the variable-length array based on the user input from lectures.
</note>

You can find testing instances {{ :courses:be5b99cpl:hw:hw2_public_v2.1.zip |here }}. Files with the suffix ''.in'' contain your input with ''.out'' your desired output.

<note tip>
When you have a file ''pub00.in'' containing the program input, you can pass it to your program in like
<code>
$ cat pub00.in | ./main
</code></note>

===== Examples =====
==== pub00 ====
^ Standard input ^ Expected output ^ Return value ^
| <code>
9
508983428
+
10
5303633367
</code> | <code>
5812616795
</code> | 0 |

==== pub03 ====
^ Standard input ^ Expected output ^ Return value ^
| <code>
25
1109945105925303633367189
-
13
5303633367189
</code> | <code>
1109945105920000000000000
</code> | 0 |

==== pub06 ====
^ Standard input ^ Expected output ^ Return value ^
| <code>
8
-53036333
*
55
-5089834282571709651070803999451059296045364409198455770
</code> | <code>
269946145925289289433504967492618198027807529912597563303491410
</code> | 0 |

==== pub07 ====
^ Standard input ^ Expected output ^ Return value ^
| <code>
19
7170965107080399945
/
10
-4505913015
</code> | <code>
-1591456622
</code> | 0 |

==== Faulty instances ====
^ Standard input ^ Expected output ^ Return value ^
| <code>
5
71709
a
10
-4505913015
</code> | <code>
Error: wrong operator
</code> | 2 |
| <code>
5
Hello
-
10
-4505913015
</code> | <code>
Error: wrong operands
</code> | 3 |
| <code>
5
71709
-
5
world
</code> | <code>
Error: wrong operands
</code> | 3 |
| <code>
abc
</code> | <code>
Error: unknown error
</code> | 1 |

===== Evaluation =====
<note>
Upload your solution into [[https://cw.felk.cvut.cz/brute/|BRUTE]] as a zip archive containing only your program's source files and either a Makefile or readme explaining how to compile it.
</note>
<note important>Your submission must compile without errors with the following compiler flags

''-Wall -Werror -pedantic -std=c99 -O2''</note>

The maximum number of points is 10. There is no automatic evaluation; you can test and verify your solution using the provided instances or generate your own.
  * 2 points - all operations with only small numbers using built-in types
  * 3 points - addition and subtraction of large numbers
  * 3 points - multiplication of large numbers
  * 2 points - coding style (structured, commented, separated into functions, meaningful naming scheme, no memory leaks etc.)

==== Bonus ====
  * 5 points - division of large numbers (round to the closest integer)

==== Late submission ====
  * **Submission is allowed by Sunday (29.10.2023) after the deadline with the following penalties:**
    * **max pts 7.5**
    * **Bonus will be only for half points (5 -> 2.5 points)**
  * Submission is allowed one week after the deadline (25.10.2023) with the following penalties:
    * 50% point reduction (10 -> 5 points)
    * Bonus will be only for half points (5 -> 2.5 points)