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Calculator
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A simple command line calculator, with the ability to solve simple linear equations.

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Compiling and dependencies
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Simply run `make` in the root of the project directory. The executable `calc` can be
found in the 'bin' subdirectory.

In order to run the test suite for the project, there are two dependencies:
1. CUunit (required)
2. Valgrind (optional)
CUnit is required for compilation and running of test suite. Valgrind is used for an
in-depth memory usage analysis.
In order to compile the test suite, run:
`make test`
The executable `suite` can be found in the 'test' subdirectory.
To run valgrind memory test with the test suite, you can:
1. make valgrind
2. run manually `valgrind ./test/suite` from the command line

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Command line arguments
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* -i <file>	Will use <file> instead of standard input.
* -o <file>	Will use <file> instead of standard output.
* -e <file>	Will use <file> instead of standard error, and will append to it.
* -v 		Prints version number and exits.
* -h		Prints usage help and exits.

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Usage
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Calculator supports the following mathematical operators: multiplication, division,
addition, substraction and logarithm. It also supports parentheses. There is also
support for implied multiplication, such as `2x` or `8(4 - x)`. No spaces are allowed
between the leading number and the following 'x' or '(';

Calculator works in two modes: simple calculation and linear equation solving.
Simple calculations take the form of an expression, while linear equations take the form
`expression` = `expression`.

Expressions used in linear equations can have variable `x` present - the application will
try to calculate the solution for the equation without an unknown variable, but there
are only two possibilities in that case: either all numbers satisfy that equation, or none
do.

Since this is a fairly simple equation solver, variable `x` is prohibited from taking
part in division and logarithm. These operations can appear in the linear equation, but
variable `x` must not take part in them, for example: 3x + 4/2 = 18.

If the application detects that the equation is not linear, it will repert error and
stop trying to solve it, for example: 4x * (x + 2) = 8/19.

Application can be closed by inputing the EOF (end of file) with Ctrl+D.

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Future improvements
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In order to make the calculator a more complete application, several improvements could
be made:

* Unary minus operator.
* Allowing 'x' to be on the left side of the divison.
* More mathematical functions with [0..n] arguments.
* Higher order equation solver.