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

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New Contributor
Posts: 4

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

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:

 

Screen Shot 2016-06-20 at 4.16.58 PM.png

 

Thank you!!!

Super User
Posts: 17,963

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

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#p1awxgleif5wlen...

 

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

 

Super User
Posts: 5,099

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

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.

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