topic Having trouble with my do...while statement, I am not sure what I am doing wrong. in SAS Programming

Having trouble with my do...while statement, I am not sure what I am doing wrong.

drajabhathor — Mon, 20 Jun 2016 20:19:48 GMT

Hello! I was wondering if anyone knows why y=20.25 shows up in my output data although I specified "while (y<20)." I am not sure what I am doing wrong here.

data do_while_data;
y=0;
do i= 1 to 5 by 0.5 while (y<20);
y=i**2; /*values are 1, 2.25, 4, 6.25,...,16*/
output;
end;
run;
proc print data=do_while_data;
run;

Here is my output data:

Thank you!!!

Re: Having trouble with my do...while statement, I am not sure what I am doing wrong.

Reeza — Mon, 20 Jun 2016 20:41:20 GMT

You're not doing anything wrong, it's where the WHILE condition is evaluated

The expression is evaluated at the top of the loop before the statements in the DO loop are executed. If the expression is true, the DO loop iterates. If the expression is false the first time it is evaluated, the DO loop does not iterate even once.

http://support.sas.com/documentation/cdl/en/lestmtsref/68024/HTML/default/viewer.htm#p1awxgleif5wlen1pja0nrn6yi6i.htm

In your case, when it enters the loop its 16, at the end it's 20.25 so it doesn't iterate again.

Re: Having trouble with my do...while statement, I am not sure what I am doing wrong.

Astounding — Mon, 20 Jun 2016 21:17:36 GMT

When SAS hits the DO loop, y is 0. So the WHILE condition is false at that point, and the loop always iterates at least once.

After the loop iterates once, it is possible that the WHILE condition becomes false and the loop ends.