Filter by date via formula field

Hi there,

I have experience with MS Access, but am new to Crystal Reports.  I am trying to filter data by date using a formula field.  Not sure how to traverse records.  In Access you have to declare a record source but I'm not sure if that is necessary in CR since the formula field is local.  ??  Also, when I use recordnumber, it Here is where I'm at....

Local Numbervar amt;
Local Numbervar i;
Local Numbervar cnt := recordnumber;

for i := 1 to cnt do (
    if ({gl_detail1.transaction_date} >= #4/1/2013# and {gl_detail1.transaction_date} <= #4/30/2013# )  then
    (           
       amt := amt + {gl_detail1.credit};
    );
);

amt