I am getting a weird number after doing a sum and not sure how to stop it from happening

[HarfordKaren]

I have the following code that I am working with:

data waiver2(keep=pidm_key tw_amount tbraccd_detail_code tbraccd_term_code);
retain tw_amount;
set waiver;
by pidm_key tbraccd_detail_code tbraccd_term_code;
if first.tbraccd_term_code then tw_amount=0;
tw_amount + tbraccd_amt;
if last.tbraccd_term_code;
if tw_amount>= 0.01;
run;

The data that I have when I go into the tw_amount + tbraccd_amt is:

tw_amount = 464
pidm_key = 233793
tbraccd_amt = -464
TBRACCD_DETAIL_CODE = WFOS
TBBDETC_DESC = Waiver CR: MD Foster Care
TBRACCD_TERM_CODE = 201540
FIRST.pidm_key = 0
LAST.pidm_key = 1
FIRST.TBRACCD_DETAIL_CODE = 0
LAST.TBRACCD_DETAIL_CODE = 1
FIRST.TBRACCD_TERM_CODE = 0
LAST.TBRACCD_TERM_CODE = 1

After the addition my data looks like this:

tw_amount = -5.6843418860808E-14
pidm_key = 233793
tbraccd_amt = -464
TBRACCD_DETAIL_CODE = WFOS
TBBDETC_DESC = Waiver CR: MD Foster Care
TBRACCD_TERM_CODE = 201540
FIRST.pidm_key = 0
LAST.pidm_key = 1
FIRST.TBRACCD_DETAIL_CODE = 0
LAST.TBRACCD_DETAIL_CODE = 1
FIRST.TBRACCD_TERM_CODE = 0
LAST.TBRACCD_TERM_CODE = 1

What is going on & how can I avoid this as I want to change the last if statement to not = 0?

Thank you,

[Reeza]

You're running into numerical precision issues. 

Round the value before comparison.

if round(tw_amount) = 0 then ...

[HarfordKaren]

The number is a dollar amount so if I round it I will lose the cents. How do I deal with that?

[Reeza · Accepted solution]

Then round to the nearest cent...

round(variable, 0.01)