roll back code in C# sql server 2005

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C#

i m using C#,asp.net,VS 2005 and sql server 2005


this s my first command:

Int32 numToModality = Convert.ToInt32((commandToModality.ExecuteScalar()));
if (numToModality != 0)
{
    Int32 numToStudyType =Convert.ToInt32(commandToStudyType.ExecuteScalar());
    if (numToStudyType != 0)
    {
      //some message to he user
    }

    else
    {
      //i want to rollback  commandToModality command
    }
}

how to rollback commandToModality command?
any help plz?
regards
Karan