(logical_expression) while(true);commands;end while - Looping control statement. while(logical_expression) end while This is a special looping structure for use in writing procedures. Before each iteration of the loop, the logical argument of the while command is evaluated. If it is TRUE then the next iteration proceeds and the commands within the loop are executed. Otherwise execution will continue from the command following the 'end while' command. This means that commands inside the loop will be executed zero or more times. If one requires a loop that will execute at least once then the alternative repeat;...;until(condition) structure should be used instead. There are also break and continue commands for breaking out of the loop or starting the next iteration prematurely. See help looping for more details. Example: 0> i=0 0> while(i<5) 1> i=i+1 1> print i 1> end while 1> print "i is now=",i results in: 1.000000 2.000000 3.000000 4.000000 5.000000 i is now= 5.000000