What is C# equivalent of this vbnet code. Also please explain each word and its function. i need to understand whole syntax

Dim div As Integer = colIndex
Dim colLetter As String = String.Empty
Dim modnum As Integer = 0
While div > 0
modnum = (div - 1) Mod 26
colLetter = Chr(65 + modnum) & colLetter
div = CInt((div - modnum) \ 26)
End While
colStatusRange = colLetter

Also this code
Dim fs As FileStream
fs = File.Open(operatorFile, FileMode.Open, FileAccess.ReadWrite, FileShare.None)
If Not IsNothing(fs) Then : fs.Close() : End If

@Gaurav07
int div = colIndex;
string colLetter = String.Empty;
int modnum = 0;
while ((div > 0)) {
modnum = ((div - 1)
% 26);
colLetter = (((char)((65 + modnum))) + colLetter);
div = int.Parse((div - modnum));
26;
}

colStatusRange = colLetter;

FileStream fs;
fs = File.Open(operatorFile, FileMode.Open, FileAccess.ReadWrite, FileShare.None);
if (!(fs == null)) {

}

:fs.Close();

@Gaurav07
Here are brief explanations for what each line is doing. The logic is the exact same between the vb.net version and the c# version that @Achal_Sharma has provided, the only difference is some minor syntax variance.

Dim div As Integer = colIndex - creates an Integer named div and sets it equal to the value of colIndex
Dim colLetter As String = String.Empty - creates a string named colLetter and sets it to be empty
Dim modnum As Integer = 0 - creates an Integer names modnum and sets it equal to 0
While div>0 ... End While - does the operations inside the loop continuously until div is >= 0
modnum = (div - 1) Mod 26 - sets modnum equal to the remainder of (div-1) divided by 26*.
colLetter = CHR(65+modnum) & colLetter - adds an ascii character to the front of colLetter*
div = CInt((div - modnum) \ 26) - sets div equal to the integer equivalent of (div-modnum)/26
colStatusRange = colLetter - sets colStatusRange equal to colLetter

* There are some ascii tricks here that can make this confusing if you aren’t familiar. Ascii code 65 is the character ‘A’. In vb.net you can use chr(65) or ‘A’ when referencing this character. So, modnum is set equal to the index of the letter: A - 0, B - 1, etc. Then, chr(65+0) = 'A', chr(65+1)='B', etc.

For the second bit of code:
Dim fs as FileStream - create a FileStream and name it fs
fs = File.Open(operatorFile, FileMode.Open, FileAccess.ReadWrite, FileShare.None) - open the Filestream. Arguments are detailed here.
If Not IsNothing(fs) Then : fs.Close() : End If - If fs is not nothing then close it. Otherwise do nothing.

please help with below error.
image