C# Academy · Lesson

Implementation & tests

Implement Rectangle, Circle, and Triangle; add basic input guards; write tiny ad-hoc tests without a framework.

Implementation plan

Goal: Implement shapes and verify them.

Implement Rectangle, Circle, Triangle
Guard invalid inputs
Add a tiny Assert helper
Run quick checks in Main

Rectangle & Circle

Add simple guards in constructors so dimensions are positive. Keep formulas small and clear.

using System;

public interface IShape
{
  double Area();
  double Perimeter();
}

public sealed class Rectangle : IShape
{
  private readonly double _w, _h;

  public Rectangle(double w, double h)
  {
    if (w <= 0 || h <= 0) throw new ArgumentOutOfRangeException("w/h must be > 0");
    _w = w; _h = h;
  }

  public double Area() { return _w * _h; }
  public double Perimeter() { return 2 * (_w + _h); }
}

public sealed class Circle : IShape
{
  private readonly double _r;

  public Circle(double r)
  {
    if (r <= 0) throw new ArgumentOutOfRangeException("r must be > 0");
    _r = r;
  }

  public double Area() { return 3.14159 * _r * _r; }
  public double Perimeter() { return 2 * 3.14159 * _r; }
}

public class Program
{
  public static void Main(string[] args)
  {
    IShape a = new Rectangle(3, 4);
    IShape b = new Circle(2);
    Console.WriteLine("Rect A=" + a.Area() + " P=" + a.Perimeter());
    Console.WriteLine("Circ A=" + b.Area() + " P=" + b.Perimeter());
  }
}

All lessons in this course

← Back to C# Academy