arrow head https://devstree.io/arrow-head-antipattern/

1.vb

if
  if
     if
         if
             if
             end if
         end if
     end if
  end if
end if

2.cs

void DoSomething(string param1, string param2)
{
    if (param1 != null)
    {
        if (param2 != null)
        {
            if (param1 == "Foo")
            {
                if (param2 == "Bar")
                {
                    Console.WriteLine("Foo Bar!");
                }
                else
                {
                    Console.WriteLine("Not Foo Bar !");
                }
            }
            else
            {
                Console.WriteLine("Not Foo Bar !");
            }
        }
    }
}

3.cs

 void DoSomethingBetter(string param1, string param2)
 {
     if (param1 == null)
         return; // datwani return y bkay, yanish...
     if (param2 == null)
         throw new ArgumentNullException("param2");  // exception y throw bkay

     if (param1 == "Foo" && param2 == "Bar")
         Console.WriteLine("Foo Bar!");
     else
         Console.WriteLine("Not Foo Bar!");
 }

4.cs

 void DoSomethingVeryShort(string param1, string param2)
{
   if (param1 == null || param2 == null)
       return;

   if (param1 == "Foo" && param2 == "Bar")
       Console.WriteLine("Foo Bar!");
   else
       Console.WriteLine("Not Foo Bar!");
}

5.cs

void DoSomethingNoReturn(string param1, string param2)
{
    bool everythingIsOkay = param1 != null && param2 != null;

    if (everythingIsOkay)
    {
        if (param1 == "Foo" && param2 == "Bar")
            Console.WriteLine("Foo Bar!");
        else
            Console.WriteLine("Not Foo Bar!");
    }
}

6.cs

void DoSomethingNoReturn2(string param1, string param2)
{
    bool notNull = param1 != null && param2 != null;
    bool notShort = param1.Length >= 3 && param2.Length >= 3;
    bool everythingIsOkay = notNull && notShort;

    if (everythingIsOkay)
    {
        if (param1 == "Foo" && param2 == "Bar")
            Console.WriteLine("Foo Bar!");
        else
            Console.WriteLine("Not Foo Bar!");
    }
}

7.cs

void DoSomethingThirdWay(string param1, string param2)
{
    if (param1 != null && param2 != null && param1.Length >= 3 && param2.Length >= 3)
    {
        if (param1 == "Foo" && param2 == "Bar")
            Console.WriteLine("Foo Bar!");
        else
            Console.WriteLine("Not Foo Bar!");
    }
}

8.cs

void DoLoop()
{
    for (int i = 0; i < 100; i++)
    {
        for (int j = 0; j < 100; j++)
        {
            for (int k = 0; k < 100; k++)
            {
                // do something
            }
        }
    }
}

9.cs

 void DoLoop()
{
    for (int i = 0; i < 100; i++)
    {
        FunctionA();
    }
}

void FunctionA()
{
    for (int j = 0; j < 100; j++)
    {
        FunctionB();
    }
}

void FunctionB()
{
    for (int k = 0; k < 100; k++)
    {
        // do something
    }
}