It is worth mentioning though that you can also store values in C variables and make use of them, rather than storing all values in LR Parameters.
* Declare variables outside the vuser_init action - makes them global across your script available to all actions
* Declare within action - makes the variable accessablile only within that action
* Declare variable in header file - makes variable accessible to any script using that header file (though each has a private copy and the value cannot be updated other vusers).
There is one disadvantage to doing this, all LR params are stored as strings, hence you need to convert the LR Param anytime you want to use anything other than a string value.