/*****************************************************************************************************************

SAS file name: DoWhile_vs_DoUntil
File location: 
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Purpose: To demonstrate the differences between the do while and the do until loop in SAS
Author: Peter Clemmensen
Creation Date: 14/04/2019

This program supports the example page "Do While Loop vs Do Until Loop Explained in SAS" on SASnrd.com

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/* Do Until loop executes at least once */
data _null_;
   a=1;
   do until (a ne 2);
      put "This is executed even though the condition is false";
   end;
run;

data _null_;
   a=1;
   do while (a=2);
      put "This is not executed because the condition is false";
   end;
run;

/* Do While Evaluates expression at the Top, Do Until Evaluates at the Bottom */
data _null_;
   a=1;
   do while(a < 3); /* Do While loop evaluates expression at the top */
      put "Inside Loop " a=;
      a=sum(a, 1);
   end;
   put // "Outside Loop " a=;
run;

data _null_;
   a=1;
   do until(a > 3);
      put "Inside Loop " a=;
      a=sum(a, 1);
   end; /* Do Until loop evaluates expression at the bottom */
   put // "Outside Loop " a=;
run;