vnmtwo/AreaCalculator

Test task from preinterview 2

Interviewer task

Write a C# library for delivery to external clients that can calculate the area of a circle from its radius and a triangle from three sides. In addition to performance, we evaluate:

Unit-tests Easy to add other shapes Calculate the area of a figure without knowing the type of figure in compile-time Checking if a triangle is a right triangle

How to start

1. Create AreaCalculator class instance

2. Add custom formula by AddFormula(string formulaName, string formula) if needed

3. Call Calculate(string formulaName, double[] args) method

    AreaCalculator.AreaCalculator ac = new AreaCalculator.AreaCalculator();  
    ac.AddFormula("CircleByD", "{PI}*POW([d]/2,2)");  
    double[] r = ac.Calculate("CircleByD", new double[] { 10 });  
   

Available builtin formulas

1. CircleByR. Calculates circle area by radius. Requires double[1] as input, where 0 element is radius. Returns double[1], where 0 element is area;
2. TriangleBySides. Calculates triangle area by sides length. Requires double[3] as input, where 0,1,2 elements is triangle sides length. Returns double[2], where 0 element is area and 1 element is check for right triangle (0 is triangle, 1 is right triangle).

Add custom formula (string formula)

You may add custom formula by AddFormula(string formulaName, string formula) method.
May use:

1. Math functions, can be obtained by MathFuncs property. f.e.: SQRT()
2. Constants, in curly brackets, can be obtained by Constants property. f.e.: {PI}
3. Variables - one letter, in square brackets. f.e.: [x]

Also, you can combine several formulas into one by separating them with a comma. f.e. [A]+[B], [A]+[C] returns [A+B, A+C]
The results of the calculation will be returned in the corresponding elements of the output array.

Available builtin constants

1. {PI} - Pi constant

Available builtin math functions

1. SQRT() - square root function. Using: SQRT[A] = square root of [A]
2. POW() - power function. Using: POW[A, B] = a^b
3. SIN() - sinus function. Using: SIN([A]) = sinus of [A], [A] in radians.
4. COS() - cosinus function. Using: SIN([A]) = cosinus of [A], [A] in radians.

Also available:
+, -, *, /
&&, ||, ! >, <, >=, <=
==, !=
<condition>?<iftrue>:<iffalse>

Add custom formula by implementing ICalculateArea

You may add custom calculator by class that implements the ICalculateArea interface.

1. Create class that implements ICalculateArea interface.
2. Add variables as fields with FormulaFieldAttribute. Best pratice is use one capital letter for variable.
3. Assign elemens of args array to your fields in CalculateArea method. Note values in the args array correspond to the fields sorted alphabetically.
4. Write your calculator code in CalculateArea method.
5. Return double[] with your calculation results.
6. Use AddFormula(string formulaName, ICalculateArea calculator) to add instance of your class as formula.
7. Call Calculate(string formulaName, double[] args)

Example of ICalculateArea implementation:

    namespace AreaCalculator
    {
        public class QuadAreaCalculator : ICalculateArea
        {       
            [FormulaField]
            public double a;

            [FormulaField]
            public double b;

            public double[] CalculateArea(double[] args)
            {
                a = args[0];
                b = args[1];

                return new[] { a * b };
            }
        }
    }

Autogenerated documentation

See AreaCalculatorDoc.xml