Tag Archives: C#

C# source code

Security – XXE external entity attack.

XXE known ad XML eXternal Entities is an application security weakness by compromised data processed by an insecurely configured XML parser. XML files may contain the document type definition known as DTD, which describes the structure of an XML file. DTD allows us to define and use XML entities. Let’s see one example:

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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE order [
  <!ENTITY lol SYSTEM "file:///D:/texts.txt">
]>
<order>
  <itemID>&lol;</itemID>
</order>

If… Read More »

C# – First steps with C# and .NET – part 047.

Extension methods enable you to “add” methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are static methods, but they’re called as if they were instance methods on the extended type. see the official website. Let’s see one simple example:

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using System;
using System.Linq;
using System.Collections.Generic;
 
public static class ExtensionMethods
{
//public static IEnumerable<T> Filter<T>(this IEnumerable<string> myArray)
//public static int[] Filter(this IEnumerable<string> someArray)
public static IEnumerable<int> Filter(this IEnumerable<string> someArray, Func<int,bool> func)
{
return someArray.Select(i => Convert.ToInt32(i)).Where(i => func(i));
}
}
 
public class Program
{
public static void Main()
{
// https://www.youtube.com/watch?v=v_cgQzp8YHQ
Console.WriteLine("Hello World");
/*
Extension methods let us add methods to existing types without creating a new  derivated type
*/
var myArray = new int[] {1,2,3,4,5,6,7,8,9};
// Where is a extension method
var evenNumbers1 = myArray.Where(x => x % 2 == 0);
Console.WriteLine($"Even numbers1 are : {string.Join(',' , evenNumbers1)}");
var evenNumbers2 = myArray.Select(x => $"Item number : {x}");
Console.WriteLine($"Even numbers2 are : {string.Join(',' , evenNumbers2)}");
// use an class extension method
var myArrayString = new string[] {"1","2","3"};
var evenNumbers3 = myArrayString.Filter(x => x > 1).Select(x => $"Item number: {x}");
Console.WriteLine($"Even numbers3 are : {string.Join(',' , evenNumbers3)}");
}
}

In this example, you… Read More »

C# – First steps with C# and .NET – part 045.

In this tutorial, I will show you how you can multiply two matrices using the C# programming language. The full source code in C# can be found on my account on dotnetfiddle online tool. This is the source code I used:

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using System;
using System.Collections.Generic;
public class Program
{
public static void Main()
{
Console.WriteLine("Hello World");
 
int i,j,k;
int[,] A = {{1, 2}, {3, 5}, {1,1976}};
int[,] B = {{5, 10, 5}, {100, 1000, 1}};
var ARows = A.GetLength(0);  
var ACols = A.GetLength(1);  
var BRows = B.GetLength(0);  
var BCols = B.GetLength(1);
Console.WriteLine("Numebr of rows in matrix A:  " + ARows + " and number of columns in matrix A: " + ACols);
Console.WriteLine("Numebr of rows in matrix B:  " + BRows + " and number of columns in matrix B: " + BCols);
int[,] C = new int[ARows, BRows];
 
List<int> matrixDimA = new List<int>();
List<int> matrixDimB = new List<int>();
Console.WriteLine("Number of matrix A elements are :" + ARows *ACols);  
//matrixDimA.Reverse();
Console.WriteLine("Elements of matrix A elements are :");  
for (i = 0; i < ARows; i++)
{
Console.Write("[");
for (j = 0; j < ACols; j++)
{
if (j != ACols - 1)
{
Console.Write( A[i, j] + ",");
}
else
{
Console.Write( A[i, j]);
}
}
Console.WriteLine("]");
}
Console.WriteLine("Number of matrix A elements are :" + BRows *BCols);  
Console.WriteLine("Elements of matrix A elements are :");  
for (i = 0; i < BRows; i++)
{
Console.Write("[");
for (j = 0; j < BCols; j++)
{
if (j != BCols - 1)
{
Console.Write( B[i, j] + ",");
}
else
{
Console.Write( B[i, j]);
}
}
Console.WriteLine("]");
}
 
if((ARows == BCols) & (ACols == BRows))
{
Console.WriteLine("Matrix multiplication is possible because: ");
Console.WriteLine("Numebr of rows in matrix A:  " + ARows + " = with number of columns in matrix B: " + BCols);
Console.WriteLine("Numebr of columns in matrix A:  " + ACols + " = with number of rows in matrix B: " + BRows);
for (i = 0; i < ARows; i++)
{
Console.Write("[");
for (j = 0; j < BRows; j++)
{
if (j != ACols - 1)
{
C[i, j] = A[i, j] * B[j, i];
Console.Write( C[i, j] + ",");
}
else
{
C[i, j] = A[i, j] * B[j, i];
Console.Write( C[i, j]);
}
}
Console.WriteLine("]");
}
 
} else {
Console.WriteLine("Matrix multiplication rows is not possible.");
}
var CRows = C.GetLength(0);  
var CCols = C.GetLength(1);
Console.WriteLine("Number of matrix C elements are :" + CRows *CCols);  
Console.WriteLine("Elements of matrix C elements are :");  
 
for (i = 0; i < CRows; i++)
{
Console.Write("[");
for (j = 0; j < CCols; j++)
{
if (j != CCols - 1)
{
Console.Write( C[i, j] + ",");
}
else
{
Console.Write( C[i, j]);
}
}
Console.WriteLine("]");
}
}
}

This is the output:

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Hello World
Numebr of rows in matrix A:  3 and number of columns in matrix A: 2
Numebr of rows in matrix B:  2 and number of columns in matrix B: 3
Number of matrix A elements are :6
Elements of matrix A elements are :
[1,2]
[3,5]
[1,1976]
Number of matrix A elements are :6
Elements of matrix A elements are :
[5,10,5]
[100,1000,1]
Matrix multiplication is possible because:
Numebr of rows in matrix A:  3 = with number of columns in matrix B: 3
Numebr of columns in matrix A:  2 = with number of rows in matrix B: 2
[5,200]
[30,5000]
[5,1976]
Number of matrix C elements are :6
Elements of matrix C elements are :
[5,200]
[30,5000]
[5,1976]

C# – First steps with C# and .NET – part 042.

This online tool can help you to understand how C# source code works with the Just-In-Time compiler(JIT) and the Intermediate Language (IL) code generated by the C# compiler. If you switch to decompile to C# you can see more information about this simple example. This decompiles C#, compiles code, then decompiles the generated assembly as… Read More »

C# – First steps with C# and .NET – part 041.

Timer Class – Generates an event after a set interval, with an option to generate recurring events. This is easy to use, let’s see one simple example:

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using System;
using System.Timers;
 
public class Program
{
    public static void Main()
    {
        Timer timer = new Timer(200);
        timer.Elapsed += Timer_Elapsed;
        timer.Start();
        while (true)
        {
            // Infinite loop.
        }
    }
    
    private static void Timer_Elapsed(object sender, ElapsedEventArgs e)
    {
        // Use SignalTime.
        DateTime time = e.SignalTime;
        Console.WriteLine("TIME: " + time);
    }

The result is this:

Shell
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TIME: 9/2/2021 7:42:16 PM
TIME: 9/2/2021 7:42:17 PM
TIME: 9/2/2021 7:42:17 PM
TIME: 9/2/2021 7:42:17 PM
TIME: 9/2/2021 7:42:17 PM
TIME: 9/2/2021 7:42:17 PM
TIME: 9/2/2021 7:42:18 PM
TIME: 9/2/2021 7:42:18 PM
TIME: 9/2/2021 7:42:18 PM
TIME: 9/2/2021 7:42:18 PM
Fatal Error: Execution time limit was exceeded

This : Fatal Error: Execution time limit was exceeded is a protected issue from This online tool comes with these restrictions: Currently… Read More »