Chapter review

For review purposes, the complete version of the Default.aspx.cs file for this chapter, including comments, is shown in the following code block:

//using is a directive
//System is a name space
//name space is a collection of features that our needs to run
using System;
//public means accessible anywhere
//partial means this class is split over multiple files
//class is a keyword and think of it as the outermost level of grouping
//:System.Web.UI.Page means our page inherits the features of a Page
public delegate bool Compare(double x, double y);
public delegate double Multiply(double x, double y);
public partial class _Default : System.Web.UI.Page
{
    protected void Button1_Click(object sender, EventArgs e)
    {
        double x = 10, y = 25; //declare two variables
        //the two variables are accessible inside the lambda expressions
        Compare comp = (a, b) => (a == b);//define comparison lambda
        //invoke the lambda in the line below
        sampLabel.Text =
         $"{x} and {y} are equal is {comp(x, y).ToString().ToLower()}";
        //line define a lambda for multiplication
        Multiply mult = (a, b) => (a * b);
        //invoke the multiplication lambda
        sampLabel.Text += $"<br>{x}*{y} is {mult(x, y)}";
        //make array of doubles
        double[] dubsArray = new double[] { 1, 2, 3, 4, 5 };
        //actions encapsulate functions that do not return a value
        //but actions can accept arguments to operate on
        Action<double> showDouble = 
        (a) => sampLabel.Text += "&lt;br>" + (a * a);
        //it's now possible to perform the action on each d repeatedly
        foreach (var d in dubsArray)
        {
            showDouble(d);
        }
    }
}