subtracting dates

[lmyers2]

Hello, I have 2 dates and I'm trying to get the difference between them in days. One is formatted as datetime20 and the other as date9. I've tried the following and neither works. 

Format them both as date9 --> Error message, there was a problem with the format so best. was used. Not sure what best. format is or whether I needed to change the informat as well. Is the difference between 2 date9 variables come out in units of days?

data want; set have;
format evrprdttm date9.;
informat evrprdttm date9.;
days=intck('dtday', evrprdttm, adate);
run;

Reformat them both as numeric --> the revised dates come out as missing along with "diff"

data want; set have;
adate_revised=input(adate, mmddyy10.);
evrprdttm_revised=input(evrprdttm, mmddyy10.);
diff=evrprdttm_revised-adate_revised;
run;

[SASKiwi]

I suggest you try converting your SAS datetime to a date first then calculate the difference as days. Also if your SAS date / datetime already has formats applied there is no reason to apply them again.

data want; set have;
days = intck('day', datepart(evrprdttm), adate);
run;

[lmyers2]

Thanks SASKiwi - when I convert evrprdttm below from datetime20 to date9, I get lines and lines of the error message pasted just below it. In proc contents, the format converts successfully to date9 but in the data, the datetime July 3, 2020 6:15 ends up being in exponential form and the subtraction doesn't work.  If you have any ideas for why I keep getting this error, would greatly appreciate the help.

data hcuant; set more.hcu;
format evrprdttm date9.;
days=intck('day', datepart(evrprdttm), datepart(adate));
run;

ERROR: There was a problem with the format so BEST. was used.

[SASKiwi]

I think we need to confirm what the input dataset really contains. Run this and post the results.

proc contents data = more.hcu;
run;

[Patrick]

A format only defines how a value gets printed. It does not change the actual internal value. SAS Dates and Datetime values are counts of days/counts of seconds since 1/1/1960.

Any function like datepart() or intck() works on the internal values irrespective of the format. 

If evrprdttm really contains a SAS Datetime value and adate a SAS Date value then below should work:

data hcuant; 
  set more.hcu;
  days=intck('day', datepart(evrprdttm), adate);
run;

...and because SAS Date values are just counts of days since 1/1/1960 also below code will work for SAS Date values:

data hcuant; 
  set more.hcu;
  days=adate - datepart(evrprdttm);
run;