Implement a combination of numeric and character story code (C # code) under ASP.net

Asp.net| verification code to facilitate everyone to learn, modify vb.net code into C #
Contents of gif.aspx File modification
private void Page_Load (object sender, System.EventArgs e)
{
Place user code here to initialize page
Rndnum is a custom function
String vnum = Rndnum (5);
session["Vnum"] = Vnum;
Validatecode (Vnum);

}
private void Validatecode (String vnum)
{
Generate validation Code
System.Drawing.Bitmap img;
System.Drawing.Graphics G;
System.IO.MemoryStream MS;
int gheight = Convert.ToInt32 (vnum.length*11.5);
Gheight for picture width, automatically change picture width based on character length
img = new Bitmap (gheight,20);
g = Graphics.fromimage (IMG);
Draws a string within a rectangle (string, font, brush color, upper left X. Upper-Left Y)
g.DrawString (vnum,new Font ("Arial"), New SolidBrush (System.Drawing.Color.Blue), 3, 3);
ms = new MemoryStream ();
Img. Save (ms,imageformat.png);

Response.clearcontent (); Need to output image information to modify HTTP headers
Response.ContentType = "Image/gif";
Response.BinaryWrite (Ms. ToArray ());
G.dispose ();
Img. Dispose ();
Response.End ();
}

' Function name: rndnum
' function parameter: vcodenum--sets the number of digits to return a random string
' function function: a random string that produces a mixture of numbers and characters
private string rndnum (int vcodenum)
{
String Vchar = "0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,w,x,y,z";
string[] Vcarray = Vchar.split (",". ToCharArray ()); To generate an array of strings
String vnum = "";
int i;
for (i=1;i<vcodenum;i++)
{
System.Random ro = new Random ();
Double DecA = ro. Nextdouble ();
Vnum = Vnum + Vcarray[convert.toint32 (35*deca)];
}
For I=1 to Vcodenum
Randomize
Vnum=vnum & Vcarray (Int (35*rnd)) ' arrays are generally read from 0, so here's the 35*rnd
Next
return vnum;

}

Validatecode.aspx Modify Content
private void Page_Load (object sender, System.EventArgs e)
{
Place user code here to initialize page
String Vnum;
if (session["Vnum"]!= null)
{
Vnum = session["Vnum"]. ToString ();
Session.Abandon ();
viewstate["Vnum"]=vnum;

}


}

private void Button1_Click (object sender, System.EventArgs e)
{
if (Txtvalidatecode.text = = viewstate["Vnum"). ToString ())
{

lblshow.text= "Hint: Verify through";
}
Else
{
Lblshow.text= "The verification code completed is not in conformity with the given";
}
}