```
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Integrationproject
{
// This is a delegate that points to a method taking a double and returning a double
// in C this is something like typedef double (*function)(double);
// I know "function" is a reserved word in C...
delegate double function(double x);
class Program
{
class MyFunctions //all these have the same signature as my delegate
{
public double MyCubic(double x)
{
return x * x * x - 2 * x * x - x - 3;
}
public double MyLine(double x)
{
return 2 * x + 1;
}
public double Reciprocal(double x)
{
return 1/x;
}
}
/////////////////////////////////////////////////////////////////////////////////////
// Integrate a function by calculating the surface under a curve by using rectangles.
// Just exercising the delegate functions here
// Not a super way to do it, but it works in explaining delegates(I hope)
// The higher the "parts" the better the integration.
public static double IntegrateRect(double a, double b, int parts, function F)
{
double width = (b - a) / parts;
double integral = 0.0;
for (int i = 1; i <= parts; i++)
{
integral += width * F(a - 0.5 * width + i * width);
}
return integral;
}
static void Main(string[] args)
{
// make my class of functions come alive
MyFunctions funcs = new MyFunctions();
// integrate some functions between 1 and 2
Console.WriteLine("Integrate linear function between 1 and 2:");
// make f point to the MyLine function and pass it to IntegrateRect
function f = new function(funcs.MyLine);
Console.WriteLine(IntegrateRect(1.0, 2.0, 10, f));
Console.WriteLine(IntegrateRect(1.0, 2.0, 1000, f));
Console.WriteLine();
//use the Reciprocal function here
//insiders know this should be equal to ln(2)=0,6931471805599453094...
//(natural logarithm)
Console.WriteLine("Integrate reciprocal function between 1 and 2:");
IntegrateRect(1.0,2.0,10,new function(funcs.Reciprocal));
IntegrateRect(1.0, 2.0, 100, new function(funcs.Reciprocal));
IntegrateRect(1.0, 2.0, 1000, new function(funcs.Reciprocal));
Console.WriteLine();
//sin has the same signature as our delegate so it should work
Console.WriteLine("Integrate sine function between 1 and 2:");
IntegrateRect(1.0,2.0,100,new function(Math.Sin));
}
}
}
```

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