string -- changing/reading 'x' char within a string

you should be able to set values in the session by

((string)Session["PageGlobals"])[5] = 'x';

and you can read them with

char c = ((string)Session["PageGlobals"])[5];

Solar_Flare:  I am getting a compiler as follows:

((string)Session["PageGlobals"])[1] = '1';

Property or indexer 'string.this[int]' cannot be assigned to -- it is read only

the '1' does  not need to be an int (as have a row of 1's and 0's in the same string -- representing various flag states, i.e. yes or no)

Try using this;
Session["PageGlobals"])[1] = '1';
If you have all the flag in Session["PageGlobals"]) variable, example "10015110", and you want to change all 0 to 2, then try below:
Session["PageGlobals"]) = Session["PageGlobals"]).ToString().Replace("0","2");

what I am looking to achieve is change a specific value within the string length...

i.e. [1], or [4] or [7] etc..

Session["PageGlobals"][1] = "1";

or  Session["PageGlobals"][1] = '1';

Cannot apply indexing with [] to an expression of type 'object'

Check below example:
string str = "0112013434";
str = str.Substring(0, 4).Replace("1", "5") + str.Substring(5, str.Length);
Response.Write(str);
I have not tested above - check, and let me know.

need example in context of a session variable - has this been converted correctly below?

Session["PageGlobals"] = (string)Session["PageGlobals"].Substring(0, 4).Replace("1", "5") + (string)Session["PageGlobals"].Substring(5, (string)Session["PageGlobals"].Length);

if so, -- I am getting the following error message:

'object' does not contain a definition for 'Substring' and no extension method 'Substring' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?

Session["PageGlobals"] = Session["PageGlobals"].ToString().Substring(0, 4).Replace("1", "5") + Session["PageGlobals"].ToString().Substring(5, Session["PageGlobals"].ToString().Length);

avnish_tanna:  could you explain a little what this routine does exactly?

it appears to replace a character(s) with another.

what do these numbers represent?

(0, 4)
("1", "5")
5, Session["PageGlobals"].ToString().Length);

You required to replace the numbers within the variable, right? I think this was your requirement.

0,4 means It will search in first 5 characters.
"1","5" means it will replace 1 with 5 within the first 5 characters, as mentioned above.
and then we concatenate the rest of the string, which we wanted unchanged.

but there could be multiples of '1' for example... -- only need the specific character to change, which is determined by its position (as each position represents a differnet page flag I keeping track off -- button/drop-down selection states etc)

1101000110100010101  for example -- each one of these '0' '1' are to be treated as a seperate variable -- basically, I did not want to have to setup x20 session variables -- instead 1 session variable which includes all the other '1's and '0' flag states required....to save memory etc.

searching a string is not what is required as such -- as I know the specific location of each char that needs to change -- hence why want to be able to reference [1], [5] etc.

(do not want to change multile characters at the same time -- just 1 char value at a time -- i.e. not all '1's to be replaced by another value -- only change value at [x] position within string.)

If position=0 then
Session["PageGlobals"] = "1" + Session["PageGlobals"].ToString().Substring(1, Session["PageGlobals"].ToString().Length);
else if position > 0 and <length-2 then
Session["PageGlobals"] = Session["PageGlobals"].ToString().Substring(0, position) + "1" + Session["PageGlobals"].ToString().Substring(position+1, Session["PageGlobals"].ToString().Length);
else if position=Length-1 then
Session["PageGlobals"] = Session["PageGlobals"].ToString().Substring(0, Session["PageGlobals"].ToString().Length-1) + "1"

Hi amillyard,
I found a simple solution to your problem:
First assume that, your session PageGlobals has a value "0128456". And you need to replace the 3rd index value '8' to '7' so that your PageGloabls session will have a value = "0127456"
           //get a session value in string variable:-
            string s = Session["PageGlobals"].ToString();
          //Create a string builder object
            StringBuilder sb = new StringBuilder(s);
         //replace the value '8' located at position 3 to "7"
             sb = sb.Replace(s.Substring(3 ,1), "7", 1, 1);  
         //Add modified result to Session:
             Session.Add("PageGlobals", sb.ToString());
Hope this will help you.  
-Nilesh

NileshVJoshi:  ok, many thanks -- then the other way -- how do I read 'x' position within the session string?