Q:

Ignoring case sensitive in c#

I have 2 string that I am comparing but I need to avoid problem if I use upper case or lower case. 
There's any way to achieve this? 
Thanks
Here's my code:
if (userID >= 0 && fnIndex >= 0 && lnIndex >= 0)
{
for (int i = 1; i < userDataId. Length; i++)
    {
     var userData = userDataId[i].List;
         if (userData[fnIndex].ToString() == "FIRSTNAME1" &&
         userData[lnIndex].ToString() == "LASTNAME1")
         {
            userId = userData[userID].ToString();
            break;
         }
     }
}

A:

You can (and should always) do this to compare strings instead of using ==:
if (userData[fnIndex].ToString().Equals(
    "FIRSTNAME1", StringComparison. CurrentCultureIgnoreCase))

Also, "FIRSTNAME1" and "LASTNAME1" should be made into constants.